I took a few online classes recently, and this is my two cents:
Research the actual structure of the online class.
The classes I had were disasters... the "classroom" was a message board, but it didn't contain posts within threads... it would just put the newest reply at the top. So if you made a post and four replies were made to it, you'd have to wade through pages and pages of other group's posts, and... bleh.
I'll take in-class over online, but I guess if you don't mind extra reading and no real reference points with the material (like you'd get in a lecture/discussion), it could work for you.