How do I get more involved with WPMU?

Recently I posted a question,

Alexander Rohmann answered the question and I would like to thank him, the info he provided was useful.

I went back to the question I posted to thank him, but it seems once you ask a question you can’t follow-up? Is this the case or am I missing something.

Also, other people had tried to answer my question, but Alexander Rohmann solved it. Can I vote him up or post a kind word for him as I appreciate his correct solution.