I'll just finish this off for completeness
It has to be a wiki page in 1.8.2, although I've read somewhere that this will be a fully qualified URL by 1.8.3, but not sure.. Hope so
it's in 1.8.2
And there you go.
The only problems with group homepages is you have to set them up per user.
Hopefully Future versions will deal with this in a sensible and automated way.. like a "Make this group the default group for it's users unless they belong to a group which includes this group" or a "overrides the groups this group includes" rule. Which are the most logical ways of inheriting group homepage inheritance automatically really.