The screenshots you see next to the C25K blogs are from Nike+ Run. This application runs on my iPhone and is strapped to my arm during my runs. It uses GPS to track your run (or a pedometer if you are stationary running like on a treadmill). The colors you see on the trail are speed/pace indicators. Green means a good pace, red means you need to pick it up. During C25K it’s split walking/running so you’ll see a lot of both but once I’m to the point where I’m running straight through it should be mostly green. Also, on the runs where I turn around on the trail rather than run a circle you’ll see over-lap.
The web-based application is also nice and shows a lot more than the iPhone app. It’s nice to log in on occasion and check out your graphs, results etc. Mainly though I just use the iPhone app.