Microblog = smaller posts, on any topic and seriousness.
Threads - articles, more meaningful entries, longer posts. Where the OP usually expects extensive interaction with other users
For example, your post is a short question. You should get an answer and that closes the topic. In threads in this case, there should be a description of the problem, ideas for a solution, information on what causes what, etc. Or a link to such content.
EricAux
WorriedGnome