Pros
Free beer, ping pong, foozeball, Xbox, laid-back company culture, casual dress code, fantastic people to work with. Offers SOME opportunity for advancement, though it is largely merit-based--work hard, become a specialist in something, and you will get promoted vertically or horizontally.
Cons
Atrocious pay, wayyy below market value. Personal and salary reviews are done for the entire company at a set time in the year, so if you didn't join the company at the right time of the year, you will have to wait more than a year and a half sometimes in order to the raise you deserve for the work you've put in. Not everybody can advance their careers here--only the few superstars. The sales team has a high turnover rate--largely because of recycled leads, excessively cold-calling low-quality leads, and low pay, even if you perform well. Company is growing WAY too fast for its own good.