If you're going to buy this car used, you're about to get a lot of car for very little money. I purchased mine for $4000 two years ago and it is my daily driver. The car rides amazingly well and looks fantastic. After detailing it, people ask what it is and compliment it at the gas station, etc., all the time. The car looks and sounds fantastic and the engine throws you back in your seat if you put your foot in it. The car was built very well (excluding using head-bolts instead of studs, see "Improvements") and looks 50,000 miles younger than it's age. The design does not look like its from the 90's and the interior is equally impressive; very comfortable.
The car gets rid of the old "grandpa's Cadillac" notion that accompanies a Caddy. The Northstar engine is an engineering marvel except for it's one real downfall. If your okay with taking a gamble, this is an unbelievable car for the money. Driving this as my first car, people assume I'm rich or my dad is in the mafia and bought it for me. I STILL know people who to this day don't believe what I paid for it. But you must understand that the fun this car can provide can end very quickly if you wind up with a lemon. Do your research well. I wouldn't buy from a used car dealership unless there was no other option.
The head gaskets on my car did indeed fail just recently (Winter 2011/2012). I am good with cars so pulled the motor and did the repair myself. If you aren't car-savvy and plan on spending just the ticket price and no maintenance, don't buy this car. Get a Honda or something reliable. Although this vehicle is strong and fast and very good looking, reliable it is not. Once the head gasket repair is complete, the car is bullet-proof, but if not you may very well be buying a money pit. If you're good with engines or very lucky, you'll make out like a bandit. If not, you'll end up like some of the other reviewers who come on here to bash this car. You can't LIKE the STS. You have to LOVE it.