I used a heart rate monitor for one ride, it was a cheap Polaris jobby. It claimed I was doing 220ish beats going along the cannal so i just binned it.
I use it everytime I run and it has proved very valuable in monitoring progress / improvements that a stopwatch alone can't tell you it's good for my motivation
I have just got a Polar ft1 (watch only) to talk to my strap when I am swimming and provide me with basic info
At the last post - Erratic heat beat spikes can be caused by static / man made fibres / not enough sweat between you and the strap. They soon settle down after you start and are easy to spot / ignore on the plots anyway