Most probably this is not something new to regular runners and users of Garmin devices, the company is quite popular on more experienced athletes who want to log and monitor their runs/ activities, by using its set of sensors (pedometers, gps trackers etc).
At the same time, you might be using along, another service from Nike, the famous Nike+ which seems to be attracting lots of attention in these recent years - and gains lots of new users (less regular or new to running) like me. I like Nike+ a lot.
Anyway, if you want to transfer your running/activity statistics from your Garmin device to your Nike+ account - there is a free service developed by Angus Smithson, called txc2nikeplus, that can take your logging data from Garmin and update your Nike+ account. It can be found here. You can contribute if you like to his donation page here.
Happy logging...to any service...it is really nice to see your km increase.
Thanks Angus, for replying our email and your time spent developing this service.