Prós
Interesting work and staff ; good work/life balance . Less MBAs, more weekend musicians. They're pretty flexible about allowing you to work from different offices if you want to move. However, most of the action is in SF headquarters. Not a lot of dead wood staff. Most people have a sense of humor and there's less arrogance than you'd encounter at places like Google, Yahoo, etc. Office shuts down for Christmas week.
Contras
Don't expect to advance if you're not in the SF office and in engineering. Hardly any relevant employee training and the content doesn't help you on the job... you're expected to train yourself by reading old wiki pages. Some staff seem pretty clueless that we're a media company and make our money by selling advertising.