Pros
If you are new to Software, or early in your career, you have the ability to prove yourself and be promoted within the company. If you are more senior with lots of experience (and the ability to motivate very diverse teams) there is also a lot of opportunity to invest yourself into a very promising, successful startup. Competent employees receive recognition/kudos and the collaborative environment between teams is impressive. You will work with lots of kind, fun, and innovative people. If you don't learn from your teammates, you have to have blinders on!
Cons
The work/life balance in some positions can be intense. You work with really intelligent, dynamic people because the positions demand it.