During our career fair I talked to a rep from a per diem staffing company and learned some interesting things. Note* (this may obviously vary from company to company and between different per diem positions)
-pay rate was usually about $10/hr above what the f/t pay would be
-benefits such as health coverage and I believe 401k were available if you logged enough days out of the year with the per diem company
-extra bonuses were available for working for them f/t or close to it
I'm not planning to go this route, but per diem might be a good way to sample what its like to work at different places and is often times a way to get your foot in the door for getting a f/t job at a site you'd like.