Not in the Bundles directory, but I do sync my TexMate directory with
Dropbox. ~/Library/Application Support/TextMate is a symlink to
~/Dropbox/Library/Application Support/TextMate
Well, that explains why Avain never picked up any of my TM bundles (although I didn't symlink TextMate, only the subdirs, to avoid syncing the .pid file). I actually prefer it though since I've collected quite a few useless and outdated bundles over the years and this gives me a fresh start.
This might be something to mention somewhere since it's probably a pretty common practice and not something I had considered might be causing an issue.
Brandon