Technology and Cycling

In the past decade there have been huge advances in on-the-bike technology.  In addition to GPS capable bike computers, there are now bike-based power meters.  These power meters measure the power (in watts) the rider is putting out at any given moment.  Simply put, the rider who can put out the most watts per unit body weight will be the fastest.  This is reffered to as the rider's power-to-weight ratio, expressed in watts/kg.
The greatest advantage to power meters versus older training methods (ie. heart rate) is that there is no lag between your effort and the power shown.  Also, power output is independent of rider fatigue, and weather conditions, where as these variables effect the riders heart rate.
The benefits are well explained in this short video:

There are three main types of bike based power meters on the market today.  

1)  Rear wheel hub by Powertap

2)  Crank based power meter by Quarq

3)  Pedal based power meter by Garmin

All three of these power meters will pair to most wireless enabled bike computers.  The data measured by these meters is then displayed for the rider to view while riding.  Having power data while riding allows the rider to accurately pace themselves and make sure they are riding at a sustainable level.  As the prices of power meters come down I expect to see them more and more as riders realise the importance of training with power.