The service touts over 10 million accounts in Europe and has the most music available of any of the digital distributors except iTunes.
Invites are being sent out soon but you can get access to Spotify right away if you open a paid account. The Unlimited account provides you with access to all the music, unlimited, with no advertising, and the ability to organize your own music.
The Premium account gives you everything, including Spotify on your cell phone, higher quality, and an offline mode.
You can see a different overview of the account differences on the Spotify Overview page.
You can pay for a paid account with Visa, MasterCard, American Express, or PayPal or wait to get your invite. Once you have your account, you can download and install Spotify for Windows or Mac, or your mobile phone.
Are you in for Spotify or are you going with an alternative like Pandora?