A friend and colleague of mine was flying from Hawaii to Chile via LAX... and his employer's policy either allowed, or (I hope not!) required that he check a case containing several thousand dollars worth of photographic equipment. To make a long story short, said employer's policy has been updated and now requires that such things not be checked. (And said friend is now using shiny new even-more-expensive photographic equipment. *jealousy*)

My backpack just barely fits in the overhead bins on 753's and 319/320's, has to go in the FC closet on 752's, and has to be gate-checked on RJ's. I'd never check it, since it tends to contain about $4-5K worth of photographic/computer gear.