folders are a necessity.
I'm and MS guy, but the WebEx office is more practical. Using Webdav to post documents to folders is more logical, not to mention much faster.
I work with teams that include semi-technical folks. Using a website to upload files at ~30 seconds a file is retarded. Creating directories and having a synch tool go to WebDAV shares is much more usable.
If you can tack on some database functionality on top of logical folders, even better (this may be the first/only real opportunity for WinFS).