Google took the next step in it's entry into the classifieds space by integrating real estate and auto search into its general search. On Google's home page, conduct a search for "jobs", "house for sale", "apartment for rent", or "used car" and you'll receive a "Refine your search" box at the above the organic search results.  You can get the same results if you go into Google Base.

What I find so interesting is that Google is using Base results to help refine these very general queries that take place in the general search engine. But when I type in "apartments for rent San Francisco", or another other type of refinement in the query, I don't see results from Google Base. I suspect that Google is still testing to see how effective Base is for those general queries and will eventually add those search boxes into more specific queries.

What this means: if you're an auto dealer or real estate agent, get your listings into Google Base. It will be a great way to make them visible to another viable audience. Note that the Google refinement box appears above Realtor.com when you search for "houses for sale" and all the major auto sites like AutoTrader.com and Cars.com. Cars.com and ZipRealty are already uploading their listings into Google Base, as is CareerBuilder.com -- they're smart to leverage this free distribution channel. Let's see if the others follow suit.

Here are some additional screenshots: