Phil-
I haven't seen many long-term expats in town, and I only personally know a few. Many of the ones I've talked to work in Mongolia for a temporary period of time... 6 months to maybe 5 years... then head back home. I haven't been in Mongolia very long myself though, so I'm sure there's more long-term expats out there.
Internet has no restrictions that I've come across so far. You can get DSL broadband in Ulaanbaatar... it's often slower than I've been used to in the US, but at least it's fairly cheap (about 15-18 US dollars/month). Cable TV is cheap too, and there are a handful of English language channels available.
Anyway, you'll quickly find Mongolia (both the country and the people) is quite a bit different than China, so it should be a new experience for you. If you haven't already, try check some of the other Mongolia Forum threads for other helpful tips and stuff...
- Nick