I actually didn't see anyone else who looked like a fan while I was there. Matt and Tim were just standing with other pedestrians waiting to cross the street--as far as I can tell, no one was paying them any notice. (But I don't know what happened before or after I was there--I saw them for less than a minute.)

I assume Jeff was only tweeting so much because it's the first week of filming--he said he's going back to LA tomorrow. Although there are a lot of sites that track NYC TV shooting locations--if fans really want to stalk them, they'll find a way. Thankfully, most New Yorkers are pretty inured to TV shows shooting nearby, so I hope they don't get too much unwanted attention.