I have been driving my S60 AWD since July of 2007. I drive from northern New England to New York City and back every other week. This car has held up well. My fuel economy seems fine (I don't pay very close attention). The comfort of the seats has remained solid, the electronics still work fine, in short, everything is still in working order. It has handled very well in snow/sleet conditions, though I recommend engaging the W option when doing so. The trunk storage is pretty good, the rear seats, while comfortable, don't have a boatload of legroom for adults. When I got this I was considering the BMW 3 Series, the S60 and the Saab 9-3. I am still very happy I decided to get the S60.
Very nice interior, very comfortable seats. Smooth ride, handles great in poor conditions. (mine is AWD) Mileage is good for this vehicle. It's heavier than the standard S60 which makes it's road performance overall much, much better. And yes, the stereo sounds great.
I would put built in booster seats in the back seats of all Volvos, like my wife has in her XC-90, or like they have done in the newest model of the XC-70. Other than the tight legroom in the back seat, I would say this is a great car for a guy who drives a lot, needs comfort and performance.