Ever thought of running a marathon, but the race date or location didn't jibe?
Do nagging injuries prevent you from ever getting to the starting line?
Are you feeling great TODAY, and would love to run a marathon TODAY?
Then DO IT. Be a random runner!
Tell randomrunners.com about your need for speed, the distance and route, and we'll tell running enthusiasts far and wide about your impromptu race. You can set up a marathon as quick as one hour (depending on the area).
Meet new people, stay in shape, and finally check "run a marathon" off your life's to do list!
OTOH: What about a site to set up "running groups". You specify a track/expected time and how often and when the group is running (monthly, twice a week etc.). This way you give people a way to organize groups, let them communicate if they are unable to show up, talk outside of a running context etc.
You might want to look into similar sites. Off the top of my head I know of runmap.net and mapmyrun.com but there are probably a lot more like this.