Hi Stef. I'm on SingSnap as "jodimuse" and you're welcome to look me up. I haven't recorded anything since about the summer though. When I got my new studio equipment, I got a little preoccupied.
Haven't tried it out with SingSnap yet - but I think I might run into the same problem as Joe. We'll see. It's just something I do for fun when I feel like singing.
When you put something up, let us know so we can check it out!
As for whether or not it's popular in the States, well, I'm in Canada and I do find there are people from all over the world on there. There was another site similar to it that got taken over by the Sim folks ... Frankly, I just find that stuff annoying. But maybe it's just me. :) So I stuck with SingSnap.