I've been to one recently; its nothing interesting. In fact, you already know most of the stuff they tell you. They go through those interminable Green packets with useless information that is obvious in it. The women we had kept on talking about how fantastic her job was as she'd just found it (brilliant, exactly what we want to hear). Yeah, so, mine lasted about an hour and didn't really teach me anything, just that I want to get out myself in to a position that I never have to set foot in a Job Centre ever again.
I recently saw that they think the Job Centre's are friendly places to go to; the staff make it blatant that they think you are, like you said above, a second class citizen and that you are scum just because you can't find a job. There's such a stigmatism towards people on benefits - the world (particularly TSR) needs to understand that not everyone on it is an idiot or a government scrounger.
Oh, and yeah you have to go - it should tell you on the letter that if you don't it is a serious breach of your contract and that your JSA could be affected should you be absent. They do a sort of register like thing at the start, you know, just to make the fact that you don't have a job even more depressing.