sounds like you know well enough that this is a question you know the answer to.

anyway, yes - i've had bars (and stems and forks and saddles and seatposts and frames and all sorts of other stuff) fail on me.

most every failure has been preceeded by some kind of warning (which has generally allowed me to correct the problem before it caused an accident), the only exception being a selle flite saddle which had a rail snap and caused a minor crash.

i'd bet that if i had regularly pulled the saddle off to grease the rails, i'd have caught the problem, though.

i'm not saying it can't happen, but the only real catastrophic failures i've witnessed with my own eyes were caused by people who ignored problems or shirked maintenance responisibilites. for instance, if you crashed on a carbon fork or bars and they were all torn up, or some other lightweight aluminum component was bent severely, replace it asap.

anyway. the answer is that yes, bike parts and every other lightweight metal sports dohickey in the world do wear out with use and need to be maintained and checked regularly.

and though every time i'm flying down a hill at 45mph i can't help but imagine a fork blade snapping, i tune up my bike regularly and i try not to sweat it.