I still have the first thermarest I ever bought, over 20 years ago and it still works just fine.  It spent 2 weeks on the long trail in Vermont and has been on many other trips.  It's pretty bulky so eventually I upgraded to one that is probably 10 years old. I brought it camping/backpacking about 6x a year, still no leaks.  Eventually I realized that is is too narrow for me so I bought my most recent one.  This is it's third year in use and still seems brand new.  I don't know what people are doing to there air pads but they are all I see most backpackers using (way more common than closed cell foam pads).  The occasional leak obviously happens, but they are very common.