Google Base has recently been springing up in the Google main search results page. As GoodROI illustrates, a search on a keyword phrase like homes for sale for many users, brings back a special box at the top of the results. The box says; "Refine your search for homes for sale." The "homes for sale" link takes you to Google Base, below that link are two boxes, the first for location and the second for "Listing type", followed by a "search housing" button, then directly under that is a "Remember this location" check box.
If you do a search for the pattern, los angeles real estate it may show you local results, but it may also show you Google Base results, which actually provides a unique drop down under listing type. Here is a screen capture;
Just an other reminder there are many ways to reach the number one spot in Google, outside of the main organic results.