Pros
They use cutting edge technologies--cloud storage, html5, .Net 4.0 etc. If you work here, you will learn a lot about the latest and greatest. They do an excellent job of keeping up to date.
Also, they give their developers unprecedented freedom. You are free to make a name for yourself (good or bad) from day 1. That kind of goes along with being in such a small company.
Finally, everyone there is incredibly intelligent. If you continuously find yourself smarter than your peers, you'll be delighted that you no longer have to explain base concepts such as timing holes.
Cons
This is a high pressure environment because of two reasons: 1) Everyone is smart. You can't get away on your intelligence or your technical skills. You have to be at the top of your game just to keep up. 2) It's a small company. Everyone sees the fruits of your labor--from your coworker to the CEO to the support staff.
Also, you have to be very politically savvy. You have to be able to stand your ground without stepping on toes. This wasn't a problem for me, but it's something that is hard to learn if you don't already know how
Finally, their benefits are quite bad: Simple IRA, very expensive healthcare, and a vacation/sick policy from the 80s.