And how! I started creating this map of interesting / useful stuff I discovered in Tokyo. I plan to expand it in the future. Note that this was done without any external tools and without uploading anything - directly in Google Maps web interface! Also note that when someone searches for "sushi" or "roller coaster" near Tokyo (and clicks on "See user-created contents"), he now automatically finds my placemarks in this map.
Also, yesterday I created a Google Map for someone just to explain where in Prague we should meet to walk the dogs and how to get there. One placemark and one line. It took a few seconds and I deleted it afterwards. But it's much easier than explaining it using words.