Honestly, after a certain point in one's career there is a greater chance of continuing career advancement through networking than there is using a job recruiting agency. It is for this reason that LinkedIn is invaluable.
For example, in early 2008 I found out that my business unit was going to have a massive (50%) RIF so I immediately contacted several people in my LinkedIn network. Within the 2 weeks immediately following, I had 8 interviews at 5 different companies. This was, obviously, without using a recruiter who would have had to screen me, reformat my resume (and probably hack it to death), etc. Instead, the people that interviewed me already had some experience with me on a professional level and were aware of the quality of work I perform.
The trick to using LinkedIn (or LI as it's known) is to have people in your network that you've actually interacted with. Although those who call themselves LIONs (LinkedIn Open Networkers) would disagree, this actually gives your network value since in situations where you need to call upon someone for a favor they are already comfortable working with you and are thus more likely to help you out.