Imagine going on an augmented run, where instead of just listening to music or podcast, you do that, and play a computer game for the extra motivation. Every now and then you'll have to pick a virtual coin, or avoid some virtual danger. Think of Sonic the Hedgehog, where you are Sonic. Or you may run against a virtual competitor, which may very well be non other than yourself, as recorded on a previous run. At the very least you'll be able to constantly see you heart rate and the number of miles you've already completed.
Now meet AR Walker from Olympus. It's a simple HUD (and not available commercially), but it's a good start. Once AR takes hold among amateur sportsmen, it will have a real chance in entering our daily lives.
CrunchGear has some more details about it.