Cassettes are still semi-viable. Cassettes sound okay in your car if you have a good car stereo. There's so much road noise in your car a lot of things sound pretty good.
What's really nice, if you still want to listen to cassettes, is to build a playlist with Winamp that is as close to 45 minutes long as possible so you know it will fit nicely on one side of a 90 minute tape. (Don't use 120 minute tapes - too fragile.) It was always a pain in the past to figure out if the next song would fit on the tape!
Now, with computers, it's easy!