Swing by VersionTracker and check out Windowshade.

It adds window shading to Carbon apps (makes Cocoa app windows transparent, you can adjust the level of transparency) pretty cool.
...but I've registered SOOOO much more shareware under OSX than I ever did under <9
the window shade part is cool... but it only works for carbon app...

I found the transparency part to be rather annoying... after making the window transparent, the window stays on top... so you need to go through extra steps to select a window behind it. If the window behind is smaller than the one in front, and is completely covered, it's just pain in the ass.

maybe I'll register when you can use window shade for both carbon and cocoa apps...