For a first version, the iTunes music store is pretty cool.
- 200,000 songs on day 1
- Songs from 5 lables (other services may have more songs, but from fewer labels)
- Windows support coming
- International support coming
- AAC is not a proprietary format, it's part of MPEG 4.
That's not to say that there's no room for improvement, but you have to release your new products sometime. They can't be in development forever.