Extras-testing. I don't know how many because counter all advice, and like i did on the N810, I have left the repositories on. I would guess I have installed at least 5 programs from extras-testing, and possible also some updates to programs from extras that are still in extras-testing.

I prefer to have access to buggy programs over lacking functionality. Some pidgin-stuff and ebook readers I had to find in extras-testing. And when I look through the lists to find something interesting, I don't notice if programs are in extras or extras-testing.

I have avoided extras-dev. Though I believe that with a little research before you install something, you can get a good idea of the likelihood of something being bad for your installation.