You build it and the users will come.
Just to scratch my itch, I developed a service for all immigrants (http://ismyprioritydatecurrent.iklavya.com/). The service does not even show up on google results since I didn't market it at all. The only thing I did for marketing was to include it as an external link on wikipedia. And I was happy to see that 10 users signed up for the service. Just wanted to share with the community :).