Great news! Way to jump into the deep end. Interfaces are the least documented thing we have. :-) I like the clean, flat design.
I had some problems getting it to build, though. The WhiteBezel folder reference in the project refers to “SquareBezel”, so none of the files can be found. Clicking it and pointing it at WhiteBezel fixes that.
Other comments:
You should remove all the imports for files outside of the project. The Quicksilver.pch file takes care of getting most of the Apple and Quicksilver headers. By importing them yourself, you end up getting “duplicate definition” errors whenever you switch between Debug and Release.
The name “White Bezel Interface” is good for the plug-in, but the “Interface” part should be removed from the name that appears in the pop-up under Appearance. I don’t know where to set that off the top of my head, but if you’ve come this far, you can probably figure it out. (From looking at other interfaces, this might be set in Localizable.strings.)
Description should have something other than the place-holder text. The extendedDescription can probably be removed, since there isn’t much to say about interfaces.
Let us know if you have any questions.