First and foremost, thanks to Bill Dubuque for advertising this in sci.math. I have more or less given up that due to its very low signal-to-noise ratio. May be I should try and locate that thread and try to give some (moral) support. Here we stick to the math. I'm not going back!
As a relatively new user I try to list the few problems I had, while I still vaguely remember what they were about. Can't say how typical they are?
1) Creating an account did feel like a turn-off at first? What the heck is an open-ID? I'm most certainly not giving you any of my passwords used elsewhere! None of the open-ID providers looked familiar at all. For one thing, they are all based in the USA! I didn't feel too welcome at this point. Luckily I had once created a Yahoo ID for the purposes of participating in an NHL-pool that we were running at work, so that saved the day. Was it actually possible to create an account without an open-ID? That's not the impression I got!
3) Wow, now I can search for interesting questions. Why can't I comment? Oh, let's read the FAQ! Ok. I need a little bit of this reputation thing. Fine. Shouldn't be too hard. Rats, this FAQ is only designed to those, who primarily want to ask questions, and don't really know how. At this point it feels like I would mostly be answering questions, but this FAQ doesn't really help much there. What to do? Let's lurk and see how the regulars do it. Hey, I remember this guy from sci.math! Let's see! WTF? Why is he giving so many details to such an obvious homework question? What about this other? He's only giving hints. Feels more responsible. Live and learn. Post an answer. Yes, an up vote! WTF. A downvote? Did I give too much detail to an obvious homework problem? Oops, I seem to have included an answer. May be that was it? Note to self: finetune your approach. Let's try a more interesting tag. Wow, an unanswered question I can say something about!... Oops that seems to have been posted half a year ago. And the asker hasn't really been active for many a month... Hmm.
Enough blogging/streamin. Sorry about that. The other things I didn't get right away:
4) Messaging system. Well, this was explained to me in Meta, but not in the FAQ.
5) May be the FAQ should explain what kind of statistics and other data I can see by clicking my own (or anyone elses) username? Granted, it is also easy enough to learn this by the time honored method of trial and error. But it is very nice to know that there is a place that maintains a list of the discussions that I have participated in.