Grown here more than any other place in my career, 4.5 years in!
Pros
Startup environments produce champions. Go look at anyone who has worked at 3 or 4 startups and where they are in their career today, all manager level people at respected firms, or they stayed till the startup sold and were compensated accordingly. What we do is very challenging, but our clients appreciate it very much. Our vision for what we want to do in the industry is refined and balanced. Working with Jeremy as the founder has been exceptionally rewarding, and I've learned a lot from every single member on this leadership team. I've been compensated well and treated very fairly 100% of the time.
Cons
I don't think of this as a negative, but a start-up business that hasn't borrowed money from someone else to grow doesn't always have as many resources as they'd like.