What is the purpose of friending people? Can you play games together or anything? Or just compare progress?
What do the coins do, aside from look pretty? I've got a whole bunch but not sure what they are good for.
Thanks for the help!
Just for tracking progress, on both counts really, at least as far as I know. The point is to make it a little competitive, like a game, so having friends and seeing their progress can help keep you motivated, especially if you have a friend at about the same level on the same language as you. The coins, for me anyway, just give me a good goal. I try to fill up my coins everyday. If I do more, awesome, but if I keep doing less I know I'm not going to make as much progress on my learning.
Friending people also makes sense if you are interested in their posts. You can see your friends' posts in your stream.
In addition, when you ask a question in the discussion, all your followers will see it, and if one of your friends ask a question, you will see it in your stream. This makes it easier to collaborate with people, and increase the probability that you will get an answer to your questions. There are some very helpful users, who they make frequent comments regarding grammar, vocabulary, details of the language that you cannot find it easily. If you manage to locate some of them, then you will see their comments in your stream every day, and it will improve your learning experience.
I'd like to clarify: if you add people as friends, this does not mean that they necessarily follow you back. If they don't, they won't see your questions in their streams.
As for users, I can recommend Sitesurf for French, and christian and wataya for German. Be careful, though, they generate so much content that your stream will be always full :D