So I'm mid-40s and in dire need of getting fitter, if I'm to be mobile into my 50s and 60s.... Enter Nokia Sports Tracker, which runs on any S60 smartphone. On my E90, with built-in GPS, I just activate it when leaving the house for a fast walk and leave it going.
When I get back to the house, I've got every stat imaginable (I'm walking at 9 minutes per km - is that good?) and a nice KML file to import directly into Google Earth. And Sports Tracker continues to log my progress over the weeks and months. Recommended.
As to whether I'll keep it up - ask me again in 2 months!