I use mine daily
I don't really need it I suppose, but I like to see what my heartrate is while working out. On the treadmills at the gym you can't check your heartrate with the grips running faster than 5km/hr. It simply warns you not to do it and stops. Which sucks because I dont care about my heartrate at 5km/hr when I am running at 12. The chest strap is awesome though. It automatically links to the treadmill while I am running at any speed and displays on the screen, no need to use the grips at all. Also do not need the watch display as the treadmill picks it up automatically.
On another curious note, I also use My Fitness Coach on the Wii. It does not use the balance board, which is good and bad. Bad because the balance board is damn fun, but good because the workout is way WAY better using an exercise ball, step and free weights. When using the heart rate monitor once again the watch isn't required as the Wii will also automatically monitor your heart rate, and the cyber-trainer will encourage you to get your heart rate up when it slips down. It is not as exact as the treadmill or the watch, giving a range instead of the exact rate, but I find it helpful.
All in all the best 20 bucks I spent.
sirant