If you have a good recruiter (the last one I worked with was such) they'll negotiate for you. This one asked me what I was looking for, said I could get more than that, and then got even more than that for me. Just because they have industry data and like jobs to back up the negotiation.
I've had bad ones of course, I think everyone has. But the good ones can do a lot more leg work than you have time for and find you a much better situation than you could find on your own, plus play both sides to make their comission as big as possible which benefits you.
more if you as an individual are not good as negotiating (and in IT there can be a higher % of people with less than stellar social skills) then these people will negotiate on your behalf. Its their job to negotiate so if they want to place you you tell them you want $x per day and if they dont get it for you you don't do the job.
