Pros
Coming from a large enterprise, I always wanted to work for a company that was focused on the technology rather than considering IT a cost center. We get to work on cutting edge technologies internally and within the multitude of external projects. Also, 5thColumn is small enough that individuals have to opportunity to shine and provide input on the direction of the company - senior management is accessible. The future outlook is awesome so there will be a need for engineer growth as well.
Cons
There are still some minor things to work out with the logistics of a small but very quickly growing company, including the need to formalize some additional HR-related processes. This will come over time and management has made strides over the last year. Also, you will not be able to hide behind bureaucracy - individual performance is key. Personally I think this is good, but some will not.