Pros
Facebook is a great place to work. Its not often that you can say that you work on a product that you genuinely believe in in a company with great values and with the best caliber people. Facebook is such a place. Nobody at Facebook is there accidentally. The interview process is intentionally tough because Facebook would rather have more False Negatives than False Positives (ie they would rather be wrong they give someone a No Hire than be wrong when go ahead a hire someone). What this means is that you are working with some of the best people in the world. Also the values that the company believes in truly important. Its great to work for a place that is so open with its Employees. Since Facebook's product is all about Social, the company makes sure that employees feel free to express their opinions. Everyone is encouraged to weigh in on important decisions. The company structure is such that we dont get fancy titles and therefore we end up being more equal. Move fast is also important, and the company removes all obstacles from employees so that they can do their job well. Overall I love working at Facebook and would recommend it to everyone.
Cons
Since the company is focused on impact, work life balance could be better. People often feel that putting in an extra hour or two a day will increase their impact. Usually this is correct, but will cause the employee to burn out faster which the company doesnt want.