The new V3 version of the Google Maps API has just released a feature that lets developers plot up to 50,000 interactive points on a map at once, and the ability to turn those points into a heatmap on the fly. It's a remarkable feature for an already impressive product.
Google Geo Developers Blog: Map your data with the Maps API and Fusion Tables
We are looking to integrate this into some of our datasets for you to visualize crime, health ratings, property values, and more in our maps. Some of our maps contain millions of points, so this won't apply to those, but we can use a subset of our data, for example, the most recent 50,000 crimes, to show at once. We'll be putting this on Metro Mapper and our parent site, Your Mapper.