Picasa Web Albums is an album based online photo sharing service - Google+ is a post based news stream. The most obvious problem with that is: in Picasa Web Albums, the visibility/privacy is album based, in Google+ it is post based. The discrepancy between these two sharing models leads to some unfortunate crutches.
Lets begin with the biggy: unlike Facebook, Flickr or 500px, a shared photo and the post it is shared in ("activity item", ie. what shows in the stream that people who follow you will see) are disconnected on Google+. A photo can exist happily all alone in an album, and while that is not a problem, you can delete the post in which you shared a photo, but the photo itself will remain in the album - an unaware user who accidentally shared a photo with the public might embarrass him- or herself that way. You can also delete the photo from the album, and a post with a broken thumbnail will remain in your stream. A warning message pops up, but the real problem is that post and photo should be one single unit.
Instead, there are multiple types of photo-posts in Google+:
- a combined "upload and share" post via the web interface when uploading a single photo. In this case, the comments to the post are the same as the comments to the photo, but the descriptive text in the post is detached from the photo.
- an "album share" post, created for example by uploading more than one photo at once. The resulting post will combine the photo-thumbnails into a single post. Comments to such a post and the descriptive text are not connected to the shared photos in any way.
- a "photo activity" post for any photo that was not shared using (1) and that receives a +1 or a comment, for example when shared via method (2).
- a post containing a Picasa Web Albums URL that is copied & pasted into a post. The comments made in the lightbox go to the photo in that case, the comments made in the stream however go to the post (yes, it's a mess).
Because of this disconnection, it is not possible to locate the post in which the photo was shared when browsing a user's albums (I began to add the URL to the post as a self-reference in the comments of the photo so I'll be able to find it again later; it is sad that this is necessary since the "state" of the photo - whether it is already in your stream or not - is known to the service). So if you write a lengthy text along with your photo, you better put it into the caption of the photo instead of the post - anything you write in the post will be "lost" somewhere down your stream after a couple of days and/or if someone browses your albums instead of your stream.
[Google never implemented both the IPTC fields "title" and "caption" in Picasa Web Albums, like Flickr did. They only and ever used "caption" for the verbose description - but imagine how handy it would be if the caption was turned into the descriptive text of the post, and the title just that - the title of the photo.]
For that reason I stopped "sharing" my photos by uploading them with the web uploader. (which is a lame crutch in itself since it still doesn't "translate" all of the metadata properly, like the keywords - oh wait, Google+ doesn't use keywords at all anyway! ...more or than later) and "pull" them into my stream with a comment or a "self+1".
Which directly brings me to the second issue with that: there is no simple "Publish to stream" feature to push a single photo that is in an album into the stream. If you're participating in one of the countless "daily photography themes" on Google+ and wish to contribute a photo that is already in one of your albums, you can't simply "push" that photo into the stream in a new post. The only "official" way to do that is to share it again - and that creates a copy of the photo in your "Photos from Posts" album, with an entirely new set of comments and +1's.
You can use a trick: copy the Picasa Web URL of the photo (not the Google+ URL!) and paste it into the post. It will appear just like a "direct" Google+ photo-share - that's method (4) I mentioned above, so beware: the comments to the post are disconnected from the comments to the photo that way. If you however use this method to share a photo that has not previously been shared into your stream, the first comment/+1 in the "lightbox view" will pull a duplicate "photo post" - method/type (3) above - into your stream.
The only way to "somewhat" connect the comments of a post and a photo is to upload the photo through the web frontend (not the Picasa software, not the export plugin for Lightroom) and share it at the time you upload it - method (1). The post and the photo will still be disconnected, but the comments to the post will also be the comments to the photo. This process itself is so cumbersome that I stopped bothering with it. There's just no way that I do all the work of captioning and keywording twice, first in Lightroom and then in the web uploader.
Organization for no one.
Because of all that, Google seems to prefer that people share their photos one-by-one, by directly adding them to a post. That way, the photos end up in separate sub-albums in the "Photos from Posts" album, each sub-album containing one single photo. Yes, one album, one photo (unless you add multiple photos to a single post, see above). A mess? You bet. Because of that, Google+ simply hides the sub-album structure, and all the photos itself are shown in the big pile of that "Photos from Posts" album directly. In the Picasa Web Albums "back end" it's a mouseclick-orgy to "drill down" to a single photo in one of these albums. If you try to organize that mess through Picasa Web Albums, you'll be annoyed rather quickly. Promised. :P
But you have to go through it in Picasa Web Albums - because in the Google+ frontend, there is no way to organize photos at all! Half a year after launching, you still cannot move photos into albums, reorganize the order of photos in an album, etc. etc. Even Facebook has some of these features (granted, their UI is terrible for that task too).
There is also no way to categorize the photos somehow in order to virtually group them, like Flickr does so nicely with it's Sets. As it is, photos in Google+ are a giant, uncontrollable mess. Using hashtags in posts? Dream on. No categories, no keywords, no search, no organization features - nothing! Good luck in finding that one photo (and maybe it's post, see above) should you wish to edit/remove it...
Photo activity became Streamspam.
Back then, in the "good old days" of Picasa Web Albums, you would receive a notification for a comment left on a photo... if you were either the owner of the photo, or had previously commented and decided to "subscribe" to further comments. Otherwise, if you were following someone, you would be "left alone". And that's how it should be.
In Google+ however, activity on a photo creates a post in your stream. If you just uploaded 100 photos from your vacation and shared the album as a whole, every first comment or first +1 on a photo will create a full "photo post" - type (3) mentioned above - in your stream, effectively "spamming" all the recipients of the album-share. This is good as a crutch since, as I mentioned above, we don't have a "Publish to stream" feature (see above), but it's really nothing but terrible if your "Friends" circle just became unreadable because one of them shared a big album and people started commenting on it.
I call that "Streamspam". This keeps me from commenting on photos in big albums, because I don't want to spam other people's reading stream. An "antisocial" feature if you ask me. Comments on a photo should be notifications to the owner of the photo and anyone who previously commented on it -- but not spam everyone who can see the album! Imagine Picasa Web Albums would send out a notification for every comment that a photo of someone you're following receives. Or if Flickr would send you a notification every time someone comments on a photo by one of your contacts! That's what's happening in Google+ all. the. time. and it's highly annoying.
To be enjoyable in the long run, photo sharing in Google+ has a long long way to go. It would be foolhardy of me to draw any further conclusions here or give recommendations what Google's developers should or should not do.
Don't get me wrong. I enjoy being in contact with so many photographers through Google+. I made some wonderful new "cyber friends" through Google+ already. But blind "fanboyism" doesn't bring us anywhere. I'd be happy to see some of the missing features being added really soon to the service. From my point of view, it's about time. ;)