For comparison I found Muse had a stream on Ping so I checked it compared to their Twitter account. Ping's stream for them was sanitized and small. It was not personal and I assume it didn't tell me anything other than what the label wanted me to know.
With full access to my very large library including many albums purchased in ITMS, they suggested a series of artists I have no interest in.
Activity is only measured by what you purchase or review in the ITMS, not on what I actually do in iTunes. They have an opportunity to steal everyones lunch with Ping. Mirroring last.fm functionality with scrobbling and then presenting that info in the profile is a no-brainer.
When looking at my profile, I noticed that the two things it pointed as were two reviews I made in iTunes from years ago. Fresh content is king.
The interface is terrible. Navigating around Ping is a mess.
Granted this is a 1.0, but they have a lot of work to do if they want it to get serious traction and they need to loosen the content reigns a bit. Waiting for my profile pic to be approved is silly.