My wife has a 2000 S80 with 60k mi that we bought Dec 1999. We have had no significant problems. I did quite a bit of research prior to buying and I would avoid anything built prior to Sept 1999. We have been pleased with ride, handling, gas mileage, room, etc.
The only problem I have is the poor resale value. I will never buy a new Volvo again. A local high end used car dealer had a 2004 S80 2.5T with 16k mi and was asking $25,900. This on a $40k sticker originally. When I called he said my wife's car was selling at auction $8,600 to $9,800. His suggestion was that since I had the 60k service done by a top local mechanic with no problems noted, and the engine and transmisson are solid, she could drive her car another 20k mi and the value would drop little. That is what we decided to do.