I am a volunteer "system administrator" for a 500+ member computer club. We recently decided to set up a classroom trial of Windows 7 for the next year using 17 computers, all about 4 1/2 years old. (8 wireless, 9 wired - all connected a 6 year old Belkin wireless"G" router.
I expected to encounter difficulties with more than 5 or 10 PC's, especially since my networking experience is minimal. I was pleasantly suprised to get the networking setup working well in an afternoon!