Here's the deal. I ran a small company for almost 2 decades in the valley. Everyone worked with everyone else very closely. One bad apple can screw up the whole company, make everyone miserable. So I used every chunk of info I could get to make sure that a potential hire was gonna be a fit. That's just being prudent.
If you are posting on mailing lists about how you screwed your boss out of a pile of work by outsourcing it to some dude in India, yeah, not a great fit. If you are posting on facebook how you partied all week on your companies' dime while they thought you were working, yeah, not so much. Etc.
If you are in to Harley-Davidson motorcycles (which I hate), well, not gonna hold that against you, though I'll let you ride my r1200gs (every Harley guy who has taken me up on that walks away looking at that GS like that's the bike he should have gotten).
I'm somewhat surprised that people question a hiring manager looking around. If you were building a team that had to work together are you seriously telling me you wouldn't look? I'd like to hear that from anyone who has successfully built multiple teams and then have them explain why they wouldn't look.