Outsourcing Recruitment?

I am a human resources manager for a technology organization of about 150 ociates. In HR it is myself and my istant and we manage all of the HR functions. Needless to say we get pretty busy. However, I am a skeptic of using recruitment firms to help with recruitment. Here is what I have found -- They rarely meet and intervew the actual candidates, which we would have to do anyway, as well as background checks and drug screens. Most resumes presented I can find myself. They inflate the candidates expected salary. They try to "sell" candidates by instilling a false sense of urgency. They call constantly, and can be haring if you don't accept their candidates. In the past I have worked with a recruiter friend. However, recently he's been "acting like a recruiter" and it's affecting our professional relationship. Can someone give me a valid, good reason to continue to working with recruitment firms? I would love to know how the process works on the inside. Thanks.