One of my best days ever was when I realized that because I had the Garmin Forerunner 305 (with a HRM that I have never used in over 2 years--I bought the 305 vs. the 205, since it was during a rebate period and only ended up costing me $8 more) I could get the cadence/speed sensor kit and use my Garmin as both a running tool and a bike computer.

I'm a noob and have found paying attention to my cadence to keep me from using too high a gear and wearing myself out. I'm sure that I eventually won't need to pay attention, since I will become accustomed to what is appropriate cadence/effort to avoid overdoing it, but it's nice now. And the ability to see how "far" I am going while pedaling on the trainer indoors until the snow clears is sure nice, too.