Pros
Huge marquee names on your resume A lot of good people to work with who make it bearable to work so many hours A hard job that makes later jobs seem easy. Seriously, the real world outside of the walls of wsod is a lot easier to excel in when you've done your time there.
Cons
Insular culture that will attempt to emotionally involve you with your work and coworkers Complicated internal processes that take a long time to learn to be good at your job but are useless knowledge in the outside world A strange shared hallucination that wsod is some kind of extraordinary opportunity and a special place to be. It's not, or at least not anymore. Each and every project from start to "finish" is broken and a disaster. Nothing happens on time, on budget, or to the quality everyone pays lip service to providing. The entire business model is to get the sites on the servers and to overcharge clients as long as they're hosting there. Development and design work are commodities basically given away for free. Clients don't respect this work, they want it done