Listened to a talk given by one of the Firefox guys a while back and in their vision social networking would be aggregated into the browser. Seems like a good start for this open alternative.
Personally, I like keeping my online social identity sandboxed away in my browser, in a tab. If it's integrated into my browser's code, then it's harder to understand how my privacy works.
In the current situation, I just have to clear my cookies to ensure my privacy is secure.
I'm _not_ enthusiastic about a future where my browser has the functionality of specific web services built into it.