Facebook has been data mining wall posts and status updates to create relevant ads for a while now, but they are upping the ante to mine real-time conversations to instantly target ads.

If someone posts “Thinking of pizza for dinner” Domino’s could instantly serve up an ad. That potential to be present at the moment someone expresses a desire for something is a very compelling proposition for advertisers.

Facebook is testing the instant ad model among only a small group of users — a mere 1% of the base, but that’s still some 6 million people. This test could make a huge difference in how Facebook ads perform, as well as how they are perceived by users. But, this brave new world raises the usual privacy concerns and Facebook will have to be very careful not to overstep the balance or risk freaking people out.

Campaigns on Facebook have been extremely successful for many big brands, but some analytics firms, including Webtrends, claim that Facebook display ad click-through rate are abysmally low — 0.051% in 2010, or about half the industry average. Low click through rates or not, last year Facebook sold some $1,86 billion in ads, over half of which were self-serve ads purchased directly using Facebook’s targeting tools. And that number is expected to keep increasing.

I wonder what the CPC will be for a chat-triggered ad compared to the other targeting options?