Power meters are a device that have really come down in price quite a bit over the past few years and they are becoming more and more common for cyclists and triathletes alike. I began training with power myself about a year ago now and I firmly believe it is as powerful a tool as a heart rate monitor.
There is no shortage of literature out there on power meters, TrainingPeaks is a great resource for such material with a good amount of info here. Anyways, I thought I'd do a quick blog post on power meters just because its a tool even that as a cyclist for a few years I wasn't really familiar with until recently.
The power meter measures the absolute power in watts that you generate on the bike which makes it an ideal tool for training and pacing. By measuring wattage, you remove all the variables that make speed a poor measure of effort such as wind, incline/decline, heat/cold. And since power is an immediate measure of effort, you know how hard you are working in that instant as opposed to heart rate which usually lags a little bit behind the effort you apply.
The great thing about this is that you can train and race far more effectively. Most triathletes are familiar with the concept of training in heart rate zones, and to determine these zones you do threshold tests. Well with the data from a threshold test you can similarly determine your power zones and train in each zone accordingly. And accordingly you can retest through the season to see how your abilities have progressed. In January your max HR for 20 minutes may be 175bpm, and when May comes around it may still be 175 bpm. But if you've been training with power you'll know that in May at 175bpm you produce 230 watts for 20 minutes, while in January you were only producing 200 watts watts for 20 minutes.
When race day comes around you can use the data you gather in training to develop a far more thorough pacing strategy. I've been passed by many a cyclist out of T1 in a long race only to pass them later on the bike or in the run, and seen many guys mash up a hill only to blow up later on the ride. But with power I know that I can produce X watts for Y hour hours, and going up/down that hill I can stick to those watts knowing that while I'm going slower/faster, I'm still sticking to my plan and will feel good for the rest of the race after.
For the record I ride with a CycleOps Powertap Elite+ powermeter. Its an entry level get the job done sort of tool but still runs a price of about $800 online. There are other brands such as SRM and Quarq which are about $1800+. So they can get pretty pricey but the nice thing is that with a technology called ANT+ you can often skip the computer they come with and save a couple hundred bucks if you have an ANT+ compatible unit such as the Garmin 310xt.
With Polar and Garmin bringing new power meters to market in the next year or so, expect prices to come down in the next 12-18 months if you're a little gunshy on spending that dough. But at the end of the day I strongly recommend powermeters for the technically inclined or anyone racing in distances longer than Olympic. They're great tools and more and more coaches are working with them so definitely add this to the wish list.