Pros
WSOD is a great place to take your junior/mid level skill set, and hone them into a powerful and valuable asset. The environment is relaxed and informal, and opportunities are available for those that seek them out. There is a wealth of knowledge to tap into. Others are more than willing to lend a hand when it's needed, and the knowledge exchange is invaluable. You'll have a chance to work on high profile sites that will force you to build skills in performance, security, and scalability, while at the same time building your portfolio. Expectations are set high, and 80% of the time you're provided with the tools you need to be successful. If you know when/how to push back, and aren't afraid to ask for additional resources when you need them, the last 20% is workable.
Cons
The informal authority structure can lead to confusion, especially if you're the type that waits to be told what is happening. The pay is sub-par, and the hours are long. Expectations are high, and sometimes unrealistic. 50 hour weeks are standard, 60 hour weeks are not uncommon, and 70-80 hour weeks should be expected. How well you and your team handle stress, will determine how much you enjoy the job. A good team-leader/project manager can make or break the experience. Usually the project managers are great, but when they're not, it's the developers/QA that get the raw end of the deal.