I like Ghoster a lot, and have been looking for something similar for a long time.
When playing Hulu it has a "Dim Lights" feature to the right, which dims the rest of the page but not the rest of the desktop.
I'd really like an app that dims the entire screen except a specific window, or potentially, a specific box. It would be even cooler if it could do something as smart as dimming everything but a specific object on a webpage, but that seems VERY difficult to pull off (I guess if it was IE-centric... maybe you could use the MSHTML API to get down to that level?)
In any case the obvious goal is to be able to work in other dimmed windows while Hulu is playing at full brightness. Ghoster works great while Hulu is the active window, but once you switch away the opposite of the intended effect occurs.
Would you be interested in building something like that?
Thanks for all the cool apps, a real treasure trove on your page!