New version of Vista Battery Saver (beta 2) is available for download from CodePlex. Except bug fixes, there is a new feature - automatic power plan change, depends on power source you are working with. I'm really wondering, why this feature is not available in Windows Vista out-of-the-box? For example, if you are working on battery, you'd want to use Power Saver plan, however, if you are working on AC, you'd rather use Balanced or High Performance. So, Vista Battery Saver does it for you now. All you have to do is to run it and configure plan you want to use on battery and on AC.
In this version, I completely rewrite power aware routines, and now it's using only direct system API call, this way, I get rid over expensive timers. So, download it, use it and notice report all bugs discovered on CodePlex issues tracker and in comments.
Thank you. Remember, It still do not run itself after the installation. You should look into Start->Accessories menu to find and run it.