Pros: Working on something brand new, that hasn't been done before, is exciting. You're breaking new ground, solving problems that have never been solved before, and overall every day is new and different. Management is great; supportive of new ideas and willing to hear what you have to say.
Cons: The same pro could be seen as a con. You can't just come in and be taught what to do... a lot of it you are going to have to figure out yourself. So it's great for self-starters, but not as great for people who need a lot of direction.