I have a 98 Chevy Mailbu V6 with 115K on it. This is a decent used car to drive; a solid 7/10. Its pretty reliable and kind of fun to drive. And the ride is smooth. The only problems I had was a starter replacement at 65K and 2 alternator replacements (My dad buys nothing but GMs alternators always need replaced on them - luckily its a cheap repair $250). Brakes do need replaced about every 35K as well. Like other people I've had a problem with the AC switch but it easily comes back on when you fiddle with it. My car gets about 23 city and 28 highway.
The automatic transmission. GM has always made great ATs (in my opinion only Toyota rivals GM in this dept) and this car is no exception. Smooth shifting and no problems whatsoever with it.
The AC electrics. GM someday is going to have to make an alternator that lasts longer than 30K miles.