Pros
Great culture and great offices. Things move quickly and you have a lot of freedom to work on the things you want, and also on larger projects.
Cons
Some of the managers care a lot about face-to-face time and many people work more than 40 hours per week despite not getting payed overtime - putting a lot of pressure on you to work more than the required 40 hours.
Interns/contractors are generally overqualified for the pay they get, and only offer a very slight raise after the 3-month internship is over. This is a major disappointment to many considering the company is hiring very quickly (5 people per month or so - you would think they could have used that money to pay their current employees a fair wage instead of hiring so many new faces).
It also feels unfair. Management gives good pay and equity to earlier employees while newer hires are given very low compensation (despite being better qualified) and no equity. Many decide to quit after their internship because the pay raise is too low to sustain a normal living in San Francisco.
CEO can be sneaky, and will use his charm to get you to accept lower pay if he can. For example, he will say: "we're thinking of giving you between $1500 and $2000 per month", and then you say "$2000 then". Essentially you had no choice and everyone gets $2000. Don't expect much of a raise after the 3 month (actually it is a 100+ days) internship.
Don't expect equity or a high pay.