My feelings about the "intro: yay or nay?" discussion is that there is no one size fits all answer. I'm currently running a Danganrona fan RP. Most of the characters don't really know much about each other aside from what they might have read on the internet about them, if they were even inclined to do that much. But the whole point about Danganronpa is that you don't really know anyone, and anyone can turn into a killer under the right circumstances. having unfamiliarity and mistrust is all part of the fun. If my goal was to write a story about a gathering of super friends coming together to beat up "the dark one," then maybe it would have been more convenient for everyone to be childhood friends so that I could skip past early character development and get straight to the monster killing. 

Though I'll be honest, I joined a role play and got shoveled into a battle with a huge GM controlled monster right off the bat. I was a bit miffed that I didn't have time to flesh out my character. Rather than being exited that I got to the "exciting part", I felt like it was an obstacle I had to take care of so that I could continue developing my character. Perhaps the moral of the story is that we all want different things, and what we want really dictates how we'd like our first few posts to come out.