Pros: Intuitive interface
Cons: Not the best sound quality on EDGE
Incredibly good app. It auto adjusts sound quality (bitrate) depending on your connection type (WiFi, 3G or EDGE) and sounds quite good on both WiFi and 3G. To thumb up or down a song it's a single touch of the screen and it's easy to bookmark songs and artists. They also have a button to purchase the song on iTunes, all extremely well done.
The only minor annoyance was that they asked you to setup the account on a PC instead of completely within the app interface.