Kimura BJJ - Watertown, MA
I've trained at three Brazilian Jiu Jitsu places over the years, and they've all been good. This is where I'm currently training, and as a long-time lurker I figured I would finally post a review.
Great school with great instruction. Most people are strongly encouraged to compete, although I haven't yet. We seem to do well, winning a bunch of the local NAGA/GQ tournaments.
Very friendly atmosphere. Good mix of people from a variety of backgrounds, although of course Brazilian male is the dominant demographic. Typically 0-2 women per class.
If you've never tried BJJ, you should. I still find it absurdly fun, and is a nice break from staring at glowing rectangles all day.
(And yes, I did read the stickied post on ratings, so hopefully these are accurate.)