Pros
Small teams, ability to innovate, interesting problems, customer impact, respect for work/life balance (at least in SF office), quality colleagues.
Cons
Customer Obsession sometimes comes at the expense of employee quality of life. (If you inherit a buggy system and get stuck on-call often, things can be bleak). Benefits are sub-par--for example, they only match 401k contributions at 50% up to 6% of your salary and you don't actually get that unless you stick around for 3 years. On the other hand, they're proud that they offer the same benefits to people who work in fulfillment centers, so you can be happy that the company is egalitarian while regretting that other tech workers are getting a few thousand more a year in untaxed retirement money than you are.