You know, I've noticed some plastics are designed in such a manner that withing a certain passing of time they become brittle and start to crack.
Problem is this theory doesn't correlate well with glock frame crack issues. There are lots of Gen-1 17's out there with a bazillion rounds through them, and then suddenly some guy will have a much younger pistol with a fudd-grade round count (say 3000 rounds or less) that got a mysterious crack in it. I think these issues are probably some kind of quality control problems that took a long time to manifest themselves. Also, some Glock owners have never had frame cracks. I only own 5 Glocks now, but in the past I owned another 7 of them in addition to what I have now. I've had a few issues with a few of them, but I have never seen a frame crack in any of them.
-Mike