Pros
They go above and beyond with benefits and perks to keep employees happy. Flexible schedules and work-from-home for proven employees. Most employees will work on a variety of projects and will naturally acquire new jobs skills.
Cons
No day-to-day guidance or communication with supervisors. Expectations are not communicated (other than "complete this project") - but when you don't meet all their hidden expectations, you will be instantly terminated without notice. There are often no resources to get help with problems as employees are often out on assignment. No mentoring whatsoever. You must track every hour and attempt to bill a client for those hours or you are losing the company money, which can be stressful. QA department doesn't really do much, which means you have to QA everything yourself or suffer the consequences (not something they tell you).