Should I use a IT staffing agency?

Looking for permanent, full time work (not contract work).I’ve been sending out resumes on my own and have been getting some bites. Recently two IT staffing agencies (RHT and TEK Systems) contacted me. They both wanted to discuss how they can assist in my job search. I’m sure this is covered in a thread somewhere (read the one from 04), but what are pros and cons of working through a IT staffing agency?