When you're picking a hotel to stay at in an area you don't know well, the place you end up at can be arbitrary. With most travel sites, you get a list of hotels with ratings, which is helpful, but still feels confusing at times. Sites like Hipmunk aim to make the search easier. Most recently Google launched a new experiment called Hotel Finder.
Enter a location and date range you want, and a map highlights the areas that are most popular. What makes an area "popular" I'm not sure, but you can see how this could be helpful (or not). The Hotel Finder also offers additional filters in the forms of sliders for price, time, and rating. Unfortunately the highlighted overlay doesn't dynamically update yet.
But let's go back to the meaning of popular. This is the most important bit. Are areas brighter where more people stay? Do they stay in these areas because they're cheaper or because they're nicer? Is it based on searches? Why are some areas with no hotels highlighted? So many questions, too few answers, and you could very well end up in some stink hole. You do get more details on a hotel when you click on one, but that defeats the purpose of the map view.