Pros
I have worked at Decision Analyst for over 10 years, and have found it to be a very fun and rewarding experience. DAI (as we like to call it), is a small company with a cozy, and somewhat family atmosphere. But the technology we use (and build) is nothing like a small, family business. I work in the software-development side of things, and we are constantly being challenged to build new and innovative technology solutions. From highly complex survey platforms, statistical simulations, email systems, and new types of interactive and animated question-types, those are the most rewarding aspects (for me). For example, I have been able to work with a half a dozen different programming tools and languages in the past 6 months, due to the variety of marketing research projects & challenges, and that flexibility would never happen in a large company.
The culture is also awesome, and very much a family atmosphere. We work hard, but also have lots of fun, including picnics, social gatherings, parties, and even Halloween costume contests. Most managers allow employees to have very flexible schedules, including some work-at-home opportunities.
Cons
The biggest con is shared by many small businesses... with less employees and very long tenure, there are less chances for promotions and career movement. But, that has never bothered me, as job titles don't mean a lot here. Like I said above, this is a very supportive and family-based atmosphere, and most team members are great people and a blast to work with.