Join Date: Mar 2010
Location: Whittier, CA
Bikes: Specialized Roubaix
Use a cotton ball - those things snag on everything. I had a tiny little wire sticking out of the tire tread on the inside of the tube one time... took me 3 flats to find it. Another difficult to diagnose culprit can be the rim tape, but if you've been riding for a while it's not likely to be rim tape. My wife's road bike came with some cheap plastic strip that depressed into the spoke wells and she was getting flats there pretty regularly till I put velox on the rim.
Good luck, flats are frustrating.
"No self-respecting man rides 70 miles and has salad at a pizza joint!" - PhotoJoe
"I like SoCal a lot better than New Jersey" - RubeRad