no, rac.co.uk hasn't done this. That's map24.com (notice the little logo in the lower left corner). You can pay them to have that service on your site. The java version of Map24 is amazing. And yes, they've done this for a while now. Check out map24.com
But Ajax is great anyway, i've seen a few more demonstrations. Check out live search at:
http://www.1976design.com/blog/
You type in the search words, and as you type you already get the results.