I use mine daily. I drop the kids off at school at 8:30 (ten minutes before they're supposedly allowed to be there, but I'm far from the only parent pushing the time a bit), and I have to be at work by 9:00. There's a 30 minute ride between the two if I keep my speed at 20+ between the intersections, but if my speed drops by a couple of miles an hour the ride stretches to 32 minutes and I'm late to work. Knowing my speed to within a couple of miles an hour therefore makes the difference between being on time and being late.

The heart rate monitor that's integrated into my computer is mostly just for fun, though.