Go look at Brian M's CF training review where he took bone stock WE's and put them in the hands of the CF to use and abuse like their real rifles. Something about 100's of thousands of rounds going though them in stock form speaks volumes about WE's.
I've had 2 issues with my WE PDW and neither of them stopped it from shooting properly. Hinge pin fell out and the bolt catch retaining pin fell out. I had an issue with the ratech npas but that wasn't a WE issue but ratech's as the nozzle had to be modded.
edit: for the lazy!
http://www.airsoftcanada.com/showthread.php?t=119707