Quote Originally Posted by KnottedYet
I'm looking at a used bottom bracket (Campy Athena) and used front derailleur (Campy Veloce or Mirage). Each is about 1/2 the cost of new.

Are those pretty safe things to get used?
A front derailleur should be safe. I'm not really familiar with Veloce or Mirage, but my Campy Nuovo Record derailleurs that I got used in 1975 are still WONDERFUL! There's
not much to go wrong with a front derailleur, other than the spring snapping or a bolt stripping. I did break a spring in a Campy Grand Tourismo rear derailleur once, but I've never heard of a front derailleur spring snapping. If you break a spring in a front derailleur, you just ride in your smallest chainring til you get it fixed. But you should expect that top quality expensive parts will last longer than mid-level parts. Not sure what that means in this case, since I haven't used Veloce or Mirage, but I certainly wouldn't expect one to be worn out in a few years.

A used BB would be fine if you and/or the LBS inspects it and it has no visible wear. Check the spindle where the bearings ride to look for a groove or pits. Inspect the cups. Inspect the spindle ends where the crank attaches. Use brand new bearings. A well maintained BB can last for 20 years. Damage shows if you look carefully in the right places.

Quote Originally Posted by KnottedYet
Do BB's ever snap and make your cranks fall off and cause disasters?

From what I've read, older Campy BB's had a habit of coming loose. Did Athena BB's do that?
A spindle would have to be extremely worn or ridden loose for a long time before there would be danger of it snapping. I haven't heard of Campy BBs coming loose frequently. Though my fixed cup has come loose twice in 20 years. If you test the BB for play frequently, you shouldn't have a problem. And riding with a loose BB is noticeable. I do remember one guy who would round his square-tapered spindle ends, and one guy who sheared off his chainring bolts, but these were big guys who only mashed in big gears.