I know it contradicts the above experiences - and may just be the manufacturing method or product design of the particular tubes that we had trouble with, but ..

We had tubes for 23-28mm tires in our 28mm Continetal Gatorskin tandem tires. We put some 32mm Avocet Fastgrip Carbon-12 tires on and had (2) flats (within the first few days of putting the larger tires on). The flats were right where the molded section near the valve stem is - and were not on the tread side. It appeared that, although the tube could easily stretch to fit the larger tire everywhere else, in the area near the stem the stretching caused the tubes to tear. Maybe if the tubes in question don't have a seperate molded area near the valve stem (and the valve stem is more-or-less patched onto the tube) this problem won't occur. Ever since this experience we've used tubes whose indicated size range included our tire size and have never had this particular problem again.