non-steel frames and longevity
I ride aluminum frames almost exclusively and have had no problem with them.

The welds are what tend to break first on most bike you hear these horror stories about, but this can happen with any sort of weld (though some forms of welding are more effective than others), so if a bike seems to be too good of a deal to have an aluminum frame, make sure to check out the welds, for those could very well be the deal breaker.