I think everyone does nowadays . . . well, enough people from LJ. I'm seeing some LJ-inside stuff appear from time to time, so it's gotta be popular enough with this base.
I have this bad feeling that YTMND is not going to make it. In their short existence of more than 2-3000 people, like the last 2 years, they've run into trouble on more than one occasion . . . great idea, but they gotta figure out how to make the money without a bunch of pop-ups and annoying shit.
The paid account feature they're talking about sounds like a good idea, and if they include stuff that's useful in it . . . sound move.
Having all those web pages with big .gifs and .wav/.mp3s . . . starting to really tax on their costs. Also, they recently started 'killing' some pages.