Pros
*Somewhat* flexible work schedule - Everyone is encouraged to work out of our space, but as long as your stuff gets done, there's usually some flexibility if you need to run an errand or want to take a longer lunch.
Office improvement budget - all employees get a yearly budget to get treats/toys/gear for the office. Think musical instruments, froyo, etc.
Variety of projects - project length varies, but they rarely go on for more than a year, and they're usually less than 6 months. It's refreshing to be able to work on something completely new every once in a while.
The people - it's easy to say this while we're relatively small (<60), but everyone is super awesome. People hang after hours and on weekends.
Cool space.
Lots of free gear.
Time to work on "passion projects".
GREAT mentors.
Cons
Rate of change - currently we are growing insanely fast, and there have been a ton of policy changes. Some of them are great, some of them not so great. Some of them made clear, some of them quietly changed. Nothing earth shattering.
Unpredictability - sometimes you get yanked off one project and put on another, without much notice. This is a small downside working at a small company operating at full capacity. It's not necessarily bad at all, if you don't mind a little instability.
Salary still a bit low - Though it's gotten much better, I still think we are paid just slightly below average for the field. Bonuses used to be great, but those were slashed pretty hard this year, as far as I can tell (to compensate for raises).