Pros
The people that you are working with on a day-to-day basis are incredibly smart, driven, and talented. If you make a good impression, you will have these connections for the rest of your career. If you do not, you will be forgotten quickly. If you are an assistant/intern, you will learn more than you thought possible. Use your time wisely there - go to every party to network, take every meeting offered, and show you are interested in furthering your career there.
Cons
Mostly women - can get very gossipy. Money is only okay. You will be working around the clock and expected to be available all times - and you will probably feel like you're not paid enough for the amount of work you do. Also - there is not a lot of privacy. Everyone finds out everything. Finally, the CEO is very rarely involved and doesn't know everyone's name. Not cool for a company so small.