This is an interesting graphic / stat from Comscore (from Oct 07). Note that it doesn't reference the recent growth of email on social networking services like Facebook & MySpace, but still it's revealing.
Email is still a very rich (and often overlooked) source of social networking / social graph data, as is IM and SMS data as well. This is notable if only because 2 of the largest stores of this data are Yahoo & AOL, both of whom are arguably up for grabs / in play.
Also noteworthy: i didn't realize Gmail had made such gains in the space. I had assumed they were #4 behind Yahoo / MSFT / AOL, but either AOL hasn't kept up with market growth, or Gmail has substantially outperformed in acquiring users since its launch a few years back. (perhaps a bit of both).
anyway, there's more juice here for an upcoming post i'm writing about monetizing social networks, but needless to say i think i'm not alone in suggesting PEOPLE ARE UNDERVALUING EMAIL AND IM DATA when they consider its impact on social networking, referral / viral marketing, and monetization.
i'll tie all these threads together in my next post, after i finish packing up & moving. ugh.