Spotify is awesome! I've converted from Grooveshark because Spotify is so effortless, and since it lives on my desktop, it doesn't slow my browser down. But Spotify is definitely lacking some content that Grooveshark has and is not as great for discovery as Pandora was.
As long as you don't mind ads, full selection is free. It does have some discovery tools, but is mostly for people who know what they want to listen to. Very similar to Grooveshark, except Spotify has no web interface.When I first started using Spotify I loved it. But I realized I'm more about finding new artists than listening to stuff I already know I like. So I went back to mostly using Hype Machine and Pandora. Like Grooveshark, Spotify is great for parties, where you want to control the playlist.
I must admit that I had my eye on Spotify long before it arrived in the US. Unreliable quality and legality led me away from file sharing programs and torrents. Before Spotify, I used the clunky and non-intuitive web-based service, Rhapsody, to fulfill my musical needs. As soon as Spotify became available I jumped aboard and never looked back. I cannot review the free version because I have only used the premium subscription service for $10/month, and I love it. The desktop app is quick and easy to use. Music starts instantly and there is virtually no audible recognition of buffering. Mostly every song that I could ever want is available on Spotify. However, you will come across some songs that are not available. I would say 95% of the music I have looked for is available. (No Beatles, but look how long it took them to get to iTunes.) I believe the selection will keep increasing as adoption increases. The iPhone application is good but not great. It plays music fine, but I do experience some skips when navigating through other applications while simultaneously listening to music. I find myself having to close out some apps to avoid this problem. Specifically, Evernote Spotify do not mix well. I write down my workout in the gym and listen to music at the same time and I constantly receive slowed performances from both apps when working simultaneously.One of the biggest drawbacks I hear about Spotify is its lack of ability to help a user discover music. While it may never beat the magical Pandora or other services like Turntable.fm, we must realize that Spotify was not built for music discovery. However, I have discovered many new artists and tracks using what I think is Spotify's most powerful feature, Facebook integration. The social aspect of Spotify is innovative and easy. You have the option of creating playlists and "publishing" them for the world to see. This gives your Facebook friends the opportunity to subscribe to the playlists that you created. If the owner of a published playlist adds or removes a song, it is reflected on the subscribers end. This is a great way for friends to dynamically share music and keep playlists from becoming dated. You can also use websites like sharemyplaylists.com to discover and rate popular user-created playlists. One last fun feature of Spotify is the ability to send and receive songs or albums. You simply drag and drop a track or album to a friend's name and a box will appear asking for an optional message to attach, type the message or skip then click send. The sent track(s) will appear in your friend's inbox. Spotify brings music to the age of social networking in the best way. I highly recommend Spotify for all music buffs and causal listeners alike. If you are looking for a fun, legal, and powerful way to find, listen and share music, Spotify is the way to go.