They do take it seriously, yes. Honestly, too seriously for my taste. Serious RP is all well and good but it helps to have a great environment and a plot or goal.
That being said, I prefer RPGs to RPs these days. People have too much trouble setting up an RP with a set goal for what is going to happen; admittedly, this can make things predictable if everyone just tries to achieve the goal. Writing a loose plot helps, you can just make notes of certain story events and leave the rest blank - fill it in as things happen, you know how it goes. But with an RPG the goal is usually pretty clear. Do this, advance. Do that, advance. If people are RPing in the RPG (god forbid! I thought people only RPd in citybuilds!) so much the better.
...I ranted a little. I forget what I was trying to say but whatever it was, if you get it, good.
