Pros
Very interesting work, across a whole range of software. I've learned more programming at this company than in six years across Google and Amazon. My coworkers are pretty good programmers in their own rights, and my boss - the company founder - is an exceptional coder. Again, it bears repeating, I've learned a lot working here. This being an early stage startup, another benefit is that you're getting in on the ground floor or close to it. There is some serious upwards career mobility if you put the time and effort in, and you can earn a good chunk of stock options in what I believe is a very promising company.
Cons
It's a startup, sometimes you need to put in the extra hours for deadline crunches. There's also a lot debugging necessary around weird operating systems and third party tools, so if you dislike having to solve problems in other peoples' (and sometimes other company's) code, that's an issue.
