Pros
Recruiters only sent worthwhile prospective jobs with a long term contract, which was exactly what I was looking for. They convinced a company to give me a chance and negotiated a rate much higher than I was looking for. My contract was with a company with a great culture. They really listened to my priorities and concerns to make a good match. Not only do they offer benefits (unusual for a staffing company), but their health benefits are better than what's offered at most companies (PPO, 80% covered, about $40/month).
Cons
Terrible HR department. Their HR gave later dates for when my benefits start and do not understand how benefits work. I basically have to prove to them when my benefits should start by literally counting down dates from when I started and tell them how to do their job.