Pros
They allow dogs, casual work atmosphere, can be very supportive, they don't nit pick over how many hours you work so long as you're getting the work done, chance to learn much and more about the IT industry, they encourage you to get certifications which make you more marketable going forward, open discussions about career paths, young, hip environment. Lot's of social activities and opportunities to get involved in the community.
Cons
Young, hip environment also translates into lower wages. Huge pay differences across departments. Lots of turnover. Workload can get very heavy, and its not uncommon to see people skipping lunches and staying late to get things done. Uncertain career path if you're not an Account Manager. 2 year contracts to stay in certain roles which may not necessarily be in your best interest. Sink or swim mentality with new hires.