These Mapplets, often referred to as mashups, allow you to add data on top of the maps. Some of the data overlays include real estate listings, jogging trails, events and photos but are open to really anything. A list can be found here.
Since I am currently in house hunting mode, I navigated on Google Maps to the area I am looking to buy a new house in. I then clicked on “My Maps” and selected the “Google Real Estate Search” Mapplet. The first result that came up was the house I was seriously looking at from my previous searches.
This new functionality is available for Google Maps users in the US, the UK, Canada, Australia, France, Italy, Germany, Spain, Netherlands, Denmark, Finland, Norway, Sweden and Russia; and is available in the following languages: English, French, Italian, German, Spanish, Dutch, Danish, Finnish, Norwegian, Swedish, Russian and Chinese (TW).
More coverage over at Techmeme.
Postscript From Danny: Mapplets is a cool name, but many of these seem to be the traditional “mashups” that people have long offered for Google — not necessarily interactive info but instead just data overlays. That’s not a negative, of course. In fact, one big positive is that as part of the launch, you can finally access a nice directory of mashups for Google Maps from Google itself. You’ll find it here. I’ve also slightly updated the story above to reflect this.