Had mixed experiences in my dealings with agents over a few months this year.
In the end though I only actually attended two interviews and both of those were jobs I had applied to directly. This wasn't always the agent's fault but statistically I had much better luck with direct applications - 5(?) applications, 2 interviews, 1 successful. I remember speaking to at least half a dozen agents about other positions, at least 3 of which were supposed to end in interviews but never did for one reason or another. So in the end it was quite refreshing - applied on the Tuesday, got a call on Wednesday to arrange an interview, went in for that the following week and had it all wrapped up in about 8 days from start to finish.
Generally speaking most agent's loved my CV, but they weren't always so enamoured with my salary expectations, once they learned what I used to be on. I even had one cheeky so-and-so trying to tell me that the increase I was looking for was too much, and he wanted to put me forward for a different (lower paid) job to the one I'd applied for. i.e. I was being judged on current salary as opposed to qualifications and experience.
I guess the problem is that a lot of agents a) have very little knowlege in the fielde they are recruiting for; and b) a lot of applicants send out speculative, cut'n'paste applications in the hope of landing some interviews. This means that they can never be too sure how suitable you are for the job.
edit: oh, since my whole (former) department was under threat of redundancy, I've also seen how other people get treated by agents. One woman was basically told to edit her CV to include certain things so that the agent could forward it on to the company - in the end she told him where to stick it as she couldn't be arsed having 50 different copies of her CV with different experience etc listed on each.
