I've been using the Nike Plus shoe insert thingy with my ipod to track the time I spend out walking. I got this for Christmas last year and late May, I crossed through 100 miles walked. Turns out that in June I walked over 50 miles! So, I've set a goal to walk 48 miles (which gets me to 200) by the end of July.
I usually walk 5 km per walk. We'll see how it goes.