I run on the treadmill and it's not very accurate... The treadmill says i'm running at 4.5 mph which means about a 13 minute mile. However i can easily do a 3 mile run in 30 minutes and that's after swimming and biking...

It's always good to have a nice outdoor place to run that has a known distance. I go down to the local YMCA where there is a trail out front (which has a nice soft shoulder that's easy on the knees) that's exactly 1 mile long (measured with my GPS unit).