The train from Perm to Ulaan Baator took 5 days and 4 nights which although was really interesting, by the end I was glad to get off. I think if you did the whole of the Trans-Siberian trip on the train without getting off you would start to go crazy.
The Mongolians use the Trans-Siberian to go to Moscow buy loads of cheap knock-off clothes then sell them on the way back down south. Apparently there are some people who just live on the trains just jumping between the north bounds and southbound to buy and sell clothes. Its obvious that they don't actually have tickets either as there seems to be quite a few back handers to officials so they can do this!
Anyway Mongolia is a lot more friendly than Russia, the people are so much nicer and surprisingly it is also geared up for tourism a lot better.
The Ger camp was amazing, basically the site was on the Mongolian Steppes about 2 hours outside Ulaan Baator. Did a bit of horse riding(!) and spent some time with a Nomad family which was fascinating.