In reply to goatee:
Punctures can be caused by dirt/grit over time, not just be noticeable sharp objects. Give a mat a good shake off/brush down before rolling up, and wipe down occasionally, to help prevent dirt gathering which is then pressed into the fabric when you roll it up.
My Thermarest lasted well over 10 years before puncturing, and I retired it from most use then anyway as it was a bit heavy. An Alpkit mat wasn't so durable, repaired twice, but is really comfy. I've fairly recently bought a really light Exped one, which has done about 25 trips so far without a problem.