Here's an example usage for Picasa's "Graduated Tint" tool (in the effects section). When you're using your camera in Matrix metering mode and you take a photo with a high dynamic range, your camera will have a hard time to capture the entire range. Depending on the camera and how much influence you can (or are willing) to take on the shot, you'll end up with a shot like the one to the left - the details in the darker areas are okay, but the sky and the rooftops are overexposed. Thats not the fault of the photographer, its a decision the camera made in Matrix metering mode. The interesting thing is that the higher tones contain much more detail than the lower ones and this can be used to fix things afterwards in Picasa even if you're shooting "only" in JPEG (instead of Raw, which you should if you can).
The next picture shows the result. All I did was to use the graduated tint tool to apply a shade to the upper part of the picture. I did not select any fancy color (you can achieve results that look as if you had used a classic filter on your lens with that), and without selecting a specific color the graduated tint tool works like a gradient filter with neutral density (ND-grad) - since you can control the orientation, the shade and the size of the feather, you have full control!
What usually happens when you reduce the brightness (no matter if you reduce it entirely or only a part of the picture) is that the color saturation rises. In the example picture beneath, you can see that the red of the roofs is very strong now. It might be a good idea to reduce the overall saturation a little bit to fix that, but thats a matter of personal preference as well (I used to like my colors very vibrant a while ago, but now I found out that less is often more...).
Maybe this was a useful tip for someone out there. :-)
I plan to post more Picasa tips & tricks in the future as I see fit and have the time. I think that the Picasa Google Group is way overcrowded and that good tips are lost in the sheer amount of posts there, thats why I use this blog to share what I know about the program.
This is just a test post to initialize the blog and test the photo publishing feature from inside Picasa. You can find more of my photos at http://picasaweb.google.com/antermoia.The picture is a quick shot out of the window at work - the sun was hiding behind the clouds and some strong flashes of light were streaking out from behind them. Looked quite nice IMHO.