Traded it in on a new '08 Altima last week. My '01 played a large role in my deciding to stay with Nissan. If you're looking for a rock-solid, reliable, and fun to drive used sedan, the Altima SE is one of the best. No major problems, just some small niggles (described below), every car has them. Very comfortable, fuel efficient (30 mpg on the highway, at least), great around town and for long-distance cruising. If you enjoy the act of driving, don't bother with the GXE or GLE... the SE is the way to go. It may not be the quickest in a straight line, but it'll surprise you in the twisties. Overall, I was very happy with the car, kinda hated to see it go. Highly recommended.
Tight construction, crisp sporty handling with SE trim level, subtly handsome without looking boy-racerish, 6-disc in-dash CD changer standard, great fuel mileage, comfortable. Only has 155 horses, but good strong torque makes it peppier that you'd expect. Cheap to own, reliable as the tides.
Had some problems with the rear suspension bushings creaking over speed bumps in the cold. When the cooling fan ran after shutting the car off, the keyless entry remote was pretty much ineffective. Never was able to figure out a fix. Could have used another 50 horses to go with the chassis... :)