well, I'm glad to see thomas tackle bundleforge ;)

IMO, the most important thing actually is allowing for easy sharing of a bundle and quick updating of the installed bundles -- ideally just a couple of mouse clicks. easy bundle setup is trivial, and the rest is if secondary importance: the focus of the server-side development should thus be on sharing and updating.

then of course you need to take care of the UI, but I'm sure you know better than me how to handle that! ;)