Google Latitude integrates with Google Maps to publish my location via GPS and my blackerry. Google also provides the little widget in the lower left corner of the blog to show where I am right now. My intent is to turn it on from the phone when I'm on the bike so the family and others who care can follow progress during long rides.
It's not ideal. Latitude tracks history of changes which in theory could show a breadcrumb trail of where i've been. But the display gadget only shows the most recent. I can turn this little tracker on and off from my phone by changing the privacy settings. A little experimenting shows the feedback from phone to website is awfully darn close to real time. No I don't intend to leave it on all the time, just on the bike.
If I find a better tool for displaying recent history I'll update it. If anyone else uses this, or similar tools, I'd like to hear what you think.