Spotify’s business model is partially based on well targeted advertising. The targeting won’t work particularly well if users share accounts. In order to be able to keep providing you with a music service that’s great for fans as well as artists, we need to start preventing account sharing in the beta test. We still want you to be able to use your Spotify account from multiple locations, though, since that’s part of our core philosophy.
The way we have implemented this is that while you can be logged in from many places (such as your home and your office), you can only stream music to one location at a time. If you’re having breakfast and listen to Spotify at home and leave it running while taking off to work, once you’re sitting comfortably in your office chair and turn on the music again, your kitchen computer streaming Spotify music at home will be paused.
As long as you’re the only one using the account, this is fine. However, if you think someone might have gotten access to your password, now is a good time to change it.