I use Cyclemeter for my commute, as I don't actually like the "social" side of things. Getting to/from work in one piece and if possible improving my time (+health) are more than enough motivation
I have friends and colleagues who love Strava though.
Be careful with apps that need internet connection for mapping/route guidance obviously.
EddiePJ - nice tip on the My GPS Coordinates...not something I'd thought of, but makes great sense! Having quikly googled such things, seems that there are even crash sensing products such as the IceDot to consider