Great questions but I, unfortunately, don't have great data on this. (insert excuses about how we're not a big company and tracking info about candidates over long periods of time isn't often on our radar)
Here are some anecdotal/gutstimate(tm) responses to the questions I think I can speak to.
" are they in/out of a boot camp?"
Yes, a majority (~75%?) of the ones that we have done are immediately following a bootcamp.
"is this their first job / are they switching jobs? _
A majority of our interns had a previous career track for a period of time. (We've had great success with people going through transitional phases)
"how long is the internship?"
We usually cap these between 6-10 weeks.
"do they go full-time at the same place after that internship?"
Rarely. Our aim is to provide interns with an opportunity to enhance their skills and get some more experience. We'd prefer to help champion them on into their next position (elsewhere)...and that gives us the ability to do that, again, for another set of interns. (from a hiring perspective, we are trying to focus on going back out to the wider/broader talent pool for long-term hires. We feel this is important as we cultivate a diverse team).
I've been developing some strong opinions about not doing this.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.