Pros
Casual and friendly atmosphere. There's a very collaborative culture in the office. The principals listen to and respect everyone's ideas. As a small office, anyone has the chance to take great responsibilities, following through projects from beginning to end, participating in client meetings. The principals give credit to everyone who works on a project, even short-term interns, they always try their best to help former employees, i.e. recommendations and project opportunities.
Cons
Because it's a small office and there isn't a strong hierarchy, everyone in the office has to do chores like cleaning and getting supplies.
It's a very open office, you can hear everything going on, from coffee making to project meetings and phone calls. It can be distracting sometimes, ( and no headphones!) but it does helps to hear the full scope of projects instead of just assignments, and to be aware of other projects and developments in the office.