By starting a keyword campaign with Google, a text link to your careers site (please tell me you have one) will show up based on certain keywords that you bid on.  Keywords can be as low as .10 per click to $20 per click or more and the highest bidder wins, putting your text ad up at the top.  If you bid low you won't be visible on the first page in the results; and really that's where you want to be.  The text ad would be designed professionally to talk about your company and match your open position.

There are several major advantages I have seen so far to start a recruitment campaign with Google:

1. Passive vs. Active Job Seekers- While all of us know that passive job seekers are exactly the people we want to target; not many have a plan for doing so on a consistent, measurable basis.  While the "Big 3" job boards are great for getting a ton of resumes; there is definitely more of an active job seeker crowd using the sites.
2. Employment Branding- Keep in mind that you only pay when a jobseeker clicks on your ad; you are getting free views of your company name when you are not clicked on.  This is great "free" branding for your company; many times a job seeker will see your ad, remember it, and go straight to your website later on.    
3. Metrics- Almost everything you do with Google can be measured quantitatively; how many visitors, where they came from, what time, and even what browser they were using.  If ROI is important to you and you want reports to show your VP then this is pretty powerful information.
4. Driving traffic to your career site- Most of the work I do involves ways to make the career site easy to apply to, attractive, and informative.  This is another way to drive traffic straight to your site where you can capture their attention instead of a job board posting where they can be distracted easily or worse find one of your competitors instead via a banner or leaderboard ad.
5. Building an exclusive Resume Database- Keep in mind that the resumes you get from the job boards are also searchable and are called on by other recruiters from other companies in the area. How nice would it be to drive passive job seekers direct from Google directly to your site before they hit the job boards?
6. Cost per Click vs. contracts- Most of us are used to negotiating 1, 2 or even 3 year online spending contracts; with Google you can "try it out" with no contracts to keep you locked in.  I would recommend a minimum of 6 months (it takes some time to tweak your campaign to see what is working and what is not) but if you have the time and a decent budget there is not much to lose.  I would define decent as a few thousand per month to get started..

If you are not sure so far, do any job search on Google.  You will notice that most of the top bidders are the Big 3; they heavily invest in Google so you know it works already the question is why aren't you doing this??

Feel free to PM me if you have any questions, comments, etc.