Caution- this is longer than it needs to be, but if this story saves one person from going through the struggles that I've been through, then it's worth it.
In the past 1.5 months I have had an incredible amount of rear flats and it has been driving me insane. These were not just slow leaks, they have typically been major blowouts and I could never figure out what was going on. When I would change the tire, I would always check the outside and the inside of the tire for staples, glass, etc, but I could never find anything. They are older Rolf Vector wheels that I have trashed through commuting and even racing cyclocross on, and I thought that maybe I had a spoke loose that was poking through the eyelet and puncturing the tube because the blowout in the tube was so major. But upon inspection, all of the spokes were tight and in decent shape. One day, I was so fed up that I stopped off at the LBS and purchased a new tire in the middle of my commute. Oh, by the way, I commute on Continental Ultra Gator Skins (700x23c) and have always been very happy with them. But the flats coninued every so often even with the new tire.
I walked back home after my flat at 5:30am one mile after leaving home. It was 32 degrees and I also didn't want to use my one one spare tube this early in my commute (especially with the luck I've been having). I get home, change my clothes and drive to work. After work, I get home and throw the bike on the workstand that my girlfriend bought me for christmas. I carefully take the tire apart and check it several times. I check the spoke tension again. No problems anywhere. I match up the whole it the tube to the spot on the tire and wheel and I cannot find anything that might be the culprit. So I throw it back together, put it back on the bike and then pump it up to 115 psi. Since I now have a stand to put my bike on, everything is at eye level and much easier to see. This is when I notice a small portion of the tube protruding out of a small tear in the sidewall. I immediately mark the tire and relieve some of the pressure. I then spin the wheel in the bike and notice that it is very slightly out of round in one spot. When the rim passes the brakepad in that one spot, the braking surface on the wheel dips down and the breakpad just barely nicks the sidewall of the tire. It just barely touches it and isn't even audible. So my diagnosis is that over time the pad nicks the sidewall enough times to create a whole large enough for the tube to protrude at 115 psi. Then BANG! At that point, I change the tire and since the very small tear is no longer under pressure, it is not visible. I put it all back together in such a way that the tire is in a slightly different position on the rim and it is just a matter of time before it wears a new rip in the sidewall. The wheel is just slightly out of round so that I never even noticed it. So I am going to take this wheel and bury it in a very deep hole where it will never be seen again and cannot give me anymore trouble. I only wish that I had gotten that bikestand as a Thanksgiving present. Could have prevented a lot of headaches.