I've noticed a trend recently whereby social networking sites on the internet are becoming integrated into desktop applications, panel applets, and now you suggest integrating it into my browser?
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.