I haven’t seen anyone using Projects. The interface seems a bit clumsy to me as it is cumbersome to add many files, chats, decks etc.
Regarding the other comments: to me it makes a lot of sense to have groups and circles because of the aforementioned reasons, but my experience is that most users get confused by the semantics and that circles aren’t really used since there is no consistent support for circles in other apps. Until recently you only could use them for files and most people don’t know that you can now use them for deck also. But even if we would mention this fact to them there’s the problem that they don’t work with contacts, calendars, talk… You name it. The semantic confusion and the bad support together seem to be they reason why practically no one I know really adopted circles.
I think I will try to promote them in two years when one of these two problems have been adressed. Until then they aren’t of much in groupware context. (if you only work with files things might be different.)