As some of you have pointed out in recent comments, much of the imagery used in the Building Maker tool seems to be angled aerial imagery, similar to the “Bird’s Eye” imagery in Bing Maps. Google is now making that imagery available via the Maps API.
The imagery is currently only available in San Jose and San Diego, but I’d expect it will expand rather quickly. Over time, I’d expect this imagery to help expand the Building Maker areas, and ultimately help more 3D models find their way into Google Earth.
Google has already partnered with a few companies to integrate this new imagery into their sites. Orbitz is using it for hotel searches, and Redfin and Trulia are using it when they show off available real estate.
If you’re interested in developing an application that uses this data, head over to the Google Geo Developers Blog to get more information about how to implement it on your site.