ifeellondon is a "fun way to share things you like doing in your city depending on the mood you’re in". The idea is that you can get ideas about stuff to do in London which have been submitted by other people and are based around how you feel (hungover, romantic, energetic etc). He's also created one for New York.
The interface uses a Google maps mash up but it's the thought about aggregating suggestions and your own tips around particular moods which is particularly top thinking - it makes for a far more relevant list of ideas rather than having to trawl through lots of listings. As Andy says, "It’s a community. It’s a resource. It’s an experiment". I think it's also rather good.