I know that MediaTemple is very cozy with the design community. Other than that, I can't glean much from their web site that would separate them from other hosting providers. I am curious for any insight on this as well!
After taking a look at them, the only thing I could find that set them apart was cost... They're _much_ more expensive...
I think they tend to pride themselves on their service (which is pretty good I guess.. the tech people you talk to at least seem to know what they're talking about), and they emphasize their scalability. I'm not sure if those things justify the price, but I guess some people think so.
That's all I've figured out myself. Too bad no MediaTemple users have commented ... I'd honestly like to know what keeps people using them at their price!