Spotify is running for 12 hours a day, 6 days a week here and I have no complaints. I love the UI and responsivess, even on my 3Mbit ADSL line. It's everything I ever wished for in a music app.
I guess my response would be: Check your disk usage for hidden evil surprises, and give it time. It'll disappoint you. I've been a user for years and it's in the last year or so that things started going downhill. Since the release of "1.0," the redesign that replaced a ton of features with a sleek design and still hasn't caught up to older versions.