The last official comment I know of regarding group size was in response to my question at the QA session with Jeff and Brad at the Fanguard. They said then that they were "leaning toward a six person limit" on group size.
Of course, that could have changed completely by now... but I don't know of a more recent comment on it from the devs.
I suppose this would be a good opportunity to link to our
FANGUARD INFORMATION article for anyone who missed it when it was published.
