When you go for an XC loop, you can create it on there, and find how far you've gone, elevation changes and so on. Then you can save it for future reference/use. I thinks its brilliant, and could be used between people on the forums to show different routes you want to share and so on.
I use an App on the iPhone called Trails, It uses the GPS receiver and plots the ride. you can email the map and view it in Google Earth or on the Everytrail website
There is also an application for android based phones that does the same length, altitude changes, max speed, average speed etc and you can save routes http://mytracks.appspot.com/