Pros
You get to work on some big clients. CMS is pretty cleverly designed - if you put in the effort, you really get a good idea of how a professional CMS is put together. Coworkers are nice. Good neighborhood. Lots of restaurants nearby.
Cons
No roadmap for advancement. Low pay. Middling benefits. Paranoia that you're going to be the next scapegoat. Lots of micromanaging and looking over your shoulder. Little opportunity for growth. Confused management - people get promoted beyond their level of competence. Hypocritical management - giving when it makes them look good, less so when they have to deal with the consequences. Long hours. High employee turnover. You won't advance unless you give up the rest of your life. Sites are frequently unambitious - you'll spend more time trudging through someone else's old broken code than you will pursuing interesting challenges. Management promises the world to clients, and employees suffer. Company owner has a right-wing blog operated by the company (http://usainexile.com/) - you'll semi-frequently be exposed to right-wing propaganda.