Pros
I've been at more than a few companies and was initially skeptical, but TS is pretty fanstastic. It's an engineering place through and through. Almost everyone is a developer of one kind or another. The people are very smart across the board with some seriously high highs, the interactions between people are expected to be nice and open (and are -- no jerks allowed), the work is very interesting (lots of big problems to solve for sophisticated internal users in a very competitive space), opportunities for internal mobility are best I've seen by a margin, senior management are super smart, nice, and engaged engineers. Big emphasis on community and internal learning and networking, regular hackathons, talks/presentations/study groups/etc all the time, by both internal and external people. Opportunities for OSS contribution, room to experiment.. And in the middle of NYC. Hard to beat.
Cons
I've been here a year and it's hard to think of many cons. Interview process is tough to pass. It's typically far from rigid environment and there are lots of opportunities, so being a self-starter and self-motivated is pretty much a must.