Pros
They managed to have at least one client. I turned that contact into a real job. Go me! Also, they can't make you show up for work. For example, in 2 months I took off 2 days for sick, 1 day for vacation, then 2 days for vacation. It hurts my pocket book but they can't say a thing.
Kontras
They are getting at least double what you are getting. Negotiating for more money is a hard thing to do, especially because they have the job contact, and if you demand more money, they just put other people in to interview. All-in-all that is a business model that is similar to a leech. The people there are not knowledgeable about anything that doesn't involve mooching off your skills. They don't offer relevant advice, they can't communicate your skills to the hiring manager, they can't communicate what the hiring manager is actually looking for. It's funny to a degree, then after you solidify an interview, get the job, learn what is actually going on, you can't get more money, they have you in a contract. They don't negotiate after that. And finally you learn they are making $65 - 80 a hour minus what you get. We, as IT people, need more power and education in the hiring process. We are letting these staffing agencies walk all over us.