I've also had similar bad experiences, usually at large "chain" garages where turnover is probably high. I think it's one thing to pay a mechanic you trust to do some work on your car and quite another to leave your car at a chain garage where it will be prodded at by some kid fresh out of high school and then taken for a joy ride to "test" it.

It's also not uncommon for garages to under or over torque fasteners because they're in a hurry. My friend had his power steering pump come off the engine block while he was driving because the garage didn't bother torquing it properly after replacing it.