It would be useful to be able to search for groups and people with some sort of filter. There are pros you can follow on here but if you don't know their user name you can't find them, additionally there is no way to look for running groups in your area without knowing their name. At a minimum you should be able to search groups by city. To me this function would greatly enhance the social aspect of the site by drawing more people together.
Another thing that drives me crazy: once you do a search, click onto a group and hit the back button you have to redo the search again to get back to where you were... annoying and should be fixed.
Also a huge +1 for me on shoe mileage and PR customizing.