Interesting, there’s a free AppleScript-based app from Apple called Aperture Caption Palette. This slick mini-app looks suspiciously like my own Aperture Caption AppleScript that I wrote in the beginning of February.
If only I knew what things are in development at Apple, it would save me a lot of time writing duplicate products!
tow.com 
but this is one of the joys of being a developer! you can do *whatever* you want whenever you want. sure, apple made a script that has similar functionality, but you were able to satisfy your own needs immediately. besides, you could say that you were there first. =P
Just goes to prove the old adage that “Great minds think alike.” BTW, the updated functionality of the reveal verb in Aperture 2.1 now allows multiple images to be selected — very useful indeed!
Note also the Apple tool seems to require OS X 10.5.2.
(I don’t know whether they are distributing the source, so that it could be modified downwards for 10.4.)
Aperture Caption Palette is an AppleScript Studio app, so the source can’t be modified.