Is there such a thing as frame failure? Several general questions have been asked regarding how long a bike or bike frame will "last", and the gist of answers seems to be that a bike can last quite a while if the replaceable components are replaced and the bike is reasonably well maintained.

But what about the inherent structural integrity of the frame itself? Is there such a thing as a risk of sudden frame failure or disintegration after some level of use? Do bikes ever fall apart, or develop a risk of breaking or fracturing along weak points? One of my bikes has more miles on it than the car I'm turning in — and I wonder about the integrity of the car!
Yes, frames do fail even if they're not crashed or ridden excessively harshly. The only way to mitigate this problem is to inspect the frame regularly during your maintenance and cleaning. Look for cracks. When riding, pay attention to creaks and squeeks and always find the root cause (it could be a crack).

Keep in mind that:


A bad weld could hold fine for years before coming apart.
Unchecked rust can eat through steel tubes, either from the outside-in or the inside-out. Once it starts, you have to keep on top of it or it will eventually take the frame. Rust also seems to have "good taste" in tubing by preferring the pretty Italian stuff to, say, gas-pipe schwinn.
Metal fatigue can form cracks that grow slowly until the frame suddenly snaps (I've seen this personally where the chainstay meets the dropout, and on crank arms). 


Aluminum is the worst culprit for fatigue cracks. Aluminum seatposts and steerer tubes also have a tendency to develop aluminum oxide blooms that may permanently jam the seatube/steerer-tube in the frame.

Carbon typically won't survive a bad-enough crash. I've heard of long-term delamination issues, but never saw one personally. AFAIK every carbon frame "dies" in a crash or mishap that damages the frame to the point where the owner no longer trusts it. Anyone have stories about what happens to carbon that is not crashed?

For a concrete example, below is my own failure from a few years ago. It happened as I was cresting a very steep hill. I heard a loud "pop" and didn't realize what happened until I looked around and saw the chainstay separate from the dropout with each pedal stroke. This is a steel bike and was totally repairable, BTW. I didn't crash as a result (but neither was I going fast). Note the little bit of rust visible at the top of the crack. It indicates that the crack had been there for some time before the total failure.