I have started to recruit on Linked In.  I have a corporate recruiting account with them.  Here are a couple of things that I have found with recruiting on Linked In:

1. I will only contact those candidates that have selected "Career opportunties" or "job inquires" checked on their profile.
2. I have found that many people just check all of these options and don't even think about it, so I get responses saying they are not interested in making a career move.  
3. I don't always get a reply when I send an "inmail" to candidates telling them about the position. For those that don't know "inmail" is Linked In's version of an email.  But then again, I don't always get a response from the candidates I find on other traditional sites as well. 
4. If you have a specific salary range in mind, you won't be able to see what the candidate is looking for because salary isn't one of the questions asked on the profile.
5. I get responses from candidates all over the country to my job ad on Linked In, even when I select local candidates only.

I have not made a hire yet from Linked In.  I am still evaluating whether it is worth the cost.

Thank you IT HR, Linked In is a site I thought would explore.  Your tips will be helpful. 

CR