First benefits are huge, and while companies vary, here is my experience:
When the company closes for minor holidays or weather, you simply do not get paid. As a temp contractor, holidays were only the six major ones, and no vacation or sick days until I had worked X number of hours. Then they'd pay me for five days-- outright. So my paycheck was aways smaller if I took a day off. Luckily I use my husbands benefits. If you are an employee of the contractor, you receive a much better deal.
I worked at the client site, and the client let everyone know you were a contractor. They would have company parties, lunches and get togethers in the common area, but no contractors were invited. My supervisor would sneak me a plate of food. It was silly. Basically the contractors did the majority of the work, for little recognition or pay.
Still if you need a paycheck, take it. If you don't see them moving you to a permanent employee, keep looking as soon as possible.