Pros
Facebook hires comparable to the best talent I've worked with in the industry, with regards to smarts -- but also with at least a modicum of social skills :)
Enormous opportunity to influence business direction, chase after your own ideas, and really stretch yourself to your fullest potential.
Almost everything that should be provided is, without lengthy approval processes, unparalleled trust in employees at all levels (you don't need to be a bigwig to get perks).
Employees are empowered to build anything, any app, service, feature. If you are a big fan of autonomy and self-driven growth, Facebook is the place to go.
Managers don't bark orders or give commands, but spend the vast majority of their time as a support role, and encouraging leadership between engineers.
Cons
Can be intimidating at times, and coworkers definitely work a lot. Perhaps similarly to startups where everyone is motivated. You have to set your own work-life balance, but flexibility exists to allow you to do so (you never feel intimidated to have to work long hours, it's more of a self-motivation question).