I run
http://www.pp-sharers.co.uk which does something similar for PlanePlotter.
It takes a feed from the PlanePlotter server every 15 minutes with info about each sharer (code, location, last active time etc) and plots this on the public map on the home page. Users can register and then claim their share code by entering their exact latitude and longitude. In return their code is monitored for uptime/downtime and their predicted coverage is calculated too.
The combined coverage is shown on the coverage map here:
http://www.pp-sharers.co.uk/coverage. It's also possible to search for the approximate location of any ground station and see it's coverage if it has been calculated. As an example, search for some of mine: XE, Xt or ir
For privacy concerns the public maps show the user location to within 5 km whilst only the private map seen by the owner of each ground station shows their exact locations.
With a little bit of work and a feed from the VRS server I could do exactly the same for VRS users too if anyone is interested ?