What's really interesting is that you will be able to download the playlists to your cellular phones, and to automatically update them for "offline use" so that you won't have to spend tons and tons of money streaming the songs to your phone. This is great, and I welcome it warmly.
People seem to have gotten very excited about this, and Spotify's CEO said: "Hold out people. The response has been enormous. We just want to make sure to deliver a great service." at Twitter about 18:00 CEST. I hope they get it out fast, as I am quite excited myself. Though, I don't really need it before Tuesday, so anything will do.
Update from Spotify at Monday, approximately 14:00 CEST: "We’re working hard on the final touches of the mobile backend to make sure you all get a great service - the response has indeed been massive and we’re really glad for your patience. And yes, the iPhone application will work on iPod Touch as well."