I attended Bitmaker Labs' 7th Web Development Intensive cohort (June 2014–August 2014) in Toronto.
I walked in knowing AngularJS and a basic level of Ruby/Rails (self-taught for both), whereas most of my classmates had either gone through the prework (very basic HTML, CSS, JS and Ruby) or were computer science grads (worked with Java, maybe C). I was ahead of the curb going in.
And that was the way things stayed. I stayed ahead because although the coursework was not designed for my level of knowledge, it helped a lot with filling in the holes of my knowledge. Also, the exposure and immersion and the side projects I did by myself led to many more 'a-ha' moments.
As for the instructors, all of them were super helpful, but they might not be very approachable early-on (the first 2 weeks or so). Depending on the kind of student you are, you'll either spend the majority of your time with the instructor learning or troubleshooting.
I echo @notjustanymike's thoughts: Bootcamp learning is only skin deep. If you go in with a lot of background knowledge you'll deepen your knowledge. If you wait a couple of months afterwards you'll deepen your knowledge. Really try to get a sense of how things work.
During the bootcamp I landed a fun gig at a local startup. Part time, not that good of a pay ($15/hour). I wasn't in the market for a job, but had I been I definitely could have gotten into the $60-$75k in Toronto.
Let me know if there's anything else you'd like to know.