Today around noon as I was riding through Palisades Park, a little ways before the Alpine hill, my rear tire blew out. I pulled to the side, flipped my bike over, spun the wheel around and found
1) a silver thumbtack
2) a piece of glass (probably got stuck to my wet tire and got driven in)
3) the kicker, a 1" gash in my new Continental GP4000, 1/2" of which cut all the way through to the tube
While I was groaning and patching everything up, another guy rolled up, stopped, and asked, "Hey, how'd you get the flat?"
"Ran over a tack."
"I just hit a tack too! Somebody must've done this on purpose."
Granted, two occurrences might not mean much, but keep your eyes peeled. It's tough to notice the sharp stuff in between the leaves and branches that are normally scattered around.
There have been a lot of flat tires on the West Side Greenway as well due to tacks. My wife has had 2 so far. One while crossing the GWB, and one near Riverbank State Park. WCBS news did a report on them last week. Little silve carpet tacks are what my wife found.