Without a huge amount of publicity, Google has indeed rolled out what they call site targeting, which lets you bid on having your advertisement run exclusively on a specific Web site or set of Web sites. Pretty cool idea, really!

Of course, the site has to already be enrolled in the AdSense program, and if you're lucky, it might already have an Advertise on this site link supplied by Google (though the latter is still in an early beta rollout).

Most interesting is that the entire pay model for site targeting adverts on AdWords is different: it's pay by the impression, rather than pay by the click. Specifically, Google explains that "The minimum cost-per-thousand (CPM) bid for a site-targeted ad is US$1.00." That's quite different from bidding, say, $0.17/click for having your ad show up somewhere in the AdSense network, and could potentially be quite a bit more expensive for a busy site. Further, there's another important nuance: your CPM-base advert is competing with all those per-click ads for space and I'm sure you realize that Google is going to automatically select the most profitable advertisement to display. Bid wrong, and you could have a few dozen impressions on a day where the site showed thousands of advertisements to visitors. Definitely you'll want to keep a close eye on your statistics in this case, to make any adjustments -- up or down -- you'll need.

So enough discussion. How do you actually set up site targeting? It's not too hard:

1. Log in to your AdWords account
2. Go to your Campaign Summary page
3. Just below the "All Campaigns" headline you'll see "Create a new campaign" with the new option of site-targeted. Click on it.
4. Follow the handy sign-up wizard to create the campaign.

Having said that, the wizard does make it a bit confusing, because you have to jump through a lot of hoops before you can identify a specific site URL, including the obvious of creating an advert itself. Finally, some way into the process, you get to the holy grail, the input field you want:

Once you've specified the sites you're interested in, you'll then get information on the range of daily ad impressions that the site sees (this site, Ask Dave Taylor, for example, is shown as askdavetaylor.com, 10k-100k. If you bid $0.50 per thousand impressions, that means you could spend $5.00-$50.00 per day having your advertisement appear on this site).

While you're here, also make sure you specified a keyword or two and check out the sites that Google recommends. There's a lot of interesting competitive data mining you can do in terms of traffic levels of other Web sites, but this is also a smart way to specifically target your ad to the more popular sites in your category too.

The final step for your ad campaign is to set a Daily Budget for the new advertising program. Remember that you're paying by impression, not by click, so you need to carefully consider this number and realize that you might well pay for thousands of impressions and generate zero actual traffic to your site.

I've been running some test campaigns myself and don't yet have enough information for any conclusions, so I'd be quite interested in hearing from others about their experiences with this program.