I borrowed my dad's yesterday at the gym.
Very useful for interval training (I squash), but not that useful in between exercises to narrow down your rest in between sets to the minute. Very light on the wrist, easy to control and check periodically. If you want to know your heartrate for cardio exercises, it's easier to use than having a sweat recycled belt around your waist, that's for sure! Also counts your footsteps, but when running I think it might be inaccurate.
Easier to avoid all contact in the gym and check your mobile phone in between sets like a socially disturbed penguin like the rest of the doodooheads.
All in all, I'm gonna get me one asap. My dad bought one for 30Euro, whereas they were 200Euro new. This one came with a mobile phone contract.