- You can't run apps in the background therefore you can't build a "scrobbler" for things you listen to locally on your device - see the (shameless plug) Strands Social Player that runs on Symbian, Windows Mobile and other mobile OSes but can't be implemented on the iPhone due to their restrictions
- The SDK doesn't allow you to touch any of the local music, only streaming content (or so I've been told), so you can't build an alternative local music application that has social features built-in (who else is listening, top fans, etc.)
- No support for flash - so you can't port/expose existing flash players in the Browser
Therefore, if you are a social media company/developer that wants to do something with music you are really pretty limited to building streaming applications (much to the chagrin of AT&T I'm guessing). Unfortunately, that hinders many discovery companies and applications from doing really compelling stuff around helping people discover new content based on what they are currently listening to (locally).
As for the streaming apps, it is interesting to note the impact of their format decisions on performance (at least on EDGE).
- Last.fm is basically unlistenable on EDGE - each song buffers for an extended period of time (a minute +) so once the song starts playing back it is good but the in-between song silence is almost longer and more unlistenable than a commercial break. This is presumably a byproduct of their 128k MP3 streams (or so I think).
- Pandora *almost* will sustain a stream in my car at high speeds - I believe they are streaming 64k AAC(plus?)
- AOL *was* in a prime position to offer a great EDGE streaming use case, for many years they were supporting 16k AACplus streams for their dial-up users - I don't know if this infrastructure was abandoned or whether it was a business decision by CBS, but they disable all but terrestrial simulcasts when you are on EDGE.