My wife and I started out yesterday AM for a 40 mile out and back to a neighboring town. About 15 miles into it, I started bouncing a little. Looked down, and back tire was low, and getting lower. Pulled it off, and while inspecting the tire for the culprit, I noticed that about 30-40 percent of the tread sections were separated from the tire. Looked like petals- they were still attached at the sidewalls, just loose in the center of the tire. Found the puncture, popped in the spare tube, and headed home, nervously. Replaced all four tires, four new tubes too.
Now, what's odd/scary about this- I check the tires during or after every ride for debris- and when the tire is inflated, there's no indication that the tread sections are loose. Can't even seen the casing anywhere. These tires are a little over a (edit - two) years old, with a couple to three (edit 2.4 )thousand miles on them- Specialized Nimbus Armadillos (great tires if you're in a flat prone area like us).
Moral- I will now take the tires off the rims at the beginning/end of each season to inspect thoroughly.
If you haven't had yours off in a while, might be worthwile to take a look.
(edit- shop is sending them back to Specialized for eval- may be a defect. Lots of rubber left)