I see two key use cases that could cause trouble:
1)a co-worker turned his computer off and went home from work, the syncing couldn't complete even if only a single doc was left
2)Because there is no central server if all of my coworkers in a distributed team sync with my new shared folder at the same time, it is required that I own a connection capable of supporting that kind of traffic, because it would be almost the same as streaming a video to multiple users, not to mention that I would probably have to avoid to browse the web for pretty much anything else in the meanwhile.
As far as 2 is concerned though, that is not the case. Don't forget, it's built on top of BT. As each piece of the file gets transferred to other clients by the original machine, the other clients will be able to send those pieces out too. In theory it will be faster than a transfer from a central server.
If I have to devise some system to zip my important stuff and keep that up to date, then I may as well just use BTSync for free.