I use MySpace, YouTube, and Facebook. I actively do NOT want instant chat (ICM). The pimped pages on MySpace are a pain in the arse, you can never find the bits to click on the page. The parlava to leave messages on YouTube is maddening. The functionality on Facebook is getting less and less accessible and its use and abuse of users data is a menace. In fact, I generally create wholly fictional persona on such sites to prevent them getting at my real data.

I joined LinkedIn at a client's insistence and have not yet found anything at all for which it is useful.

As for Twotter, why do I need to know the same second that anyone has farted or how many eggs they ate for breakfast?

I also use several Volvo related sites, perhaps most notably Turbobricks.

Frankly, the usability of Mudcat is head and shoulders above any of them.