That's exactly how I got started, a guy I worked with at Pitt who commuted by bike every day (and still does, although in Davis now) got me into riding as well as a slew of other people. And hopefully I've helped a few others along the path...
I'll try to gloss over my 10 year hiatus from cycling, moving to the suburbs, etc... But I'm back in the city and riding again and at least occasionally commuting thanks to another co-worker and another old riding buddy who is now in Seattle who convinced me 10-15 miles commuting was at least possible. Most people in the office think I'm crazy but I know at least one guy is out looking at bikes...
So, I do think having some sort of support, comradery, etc. is important in getting people into biking, and it definitely feeds off itself.