I've now driven almost 7000 miles with my S80 V8. No mechanical or other problems. Sound of the V8 is great, very civil background roar without getting obnoxious. Mileage isn't so bad, with average driving (city and commute), I get 24mpg highway and 18mpg real average. Don't agree the body styling is boring. The old S80 was pretty boring but the 2007 & up model has a nice refined look, to my taste.
I also considered the A6 3.2 and the 528, but even with the V8 and almost all options (navigation, rear seat entertainment, premium sound, the works), the invoice price of the S80 was $12,000 less than a loaded A6 or BMW. My perception of the overall qualtiy and value of the car is great.
Only consideration to take is that the S80 is more a luxury sedan than a sports sedan like a A6 or 5-series. Ride could be a bit more stiff and direct. But it certainly isn't bad, considering that I drive it (boringly) at 65mph cruise controle highway commute anyhow.