First Cari: Welcome to the board. There's a thread under the open titled "getting to know you" gives you a chance to meet us and if you feel so inclined tell us something about you!
Re: your question, I actually don't have an HRM. I've been kicking around the idea of getting one but I don't intend on racing, I can Tell I'm losing body fat/weight and I KNOW when my heart is pouding! LOL
Now Cadence: Love it!! I keep my computer set on the cadence and rarely look at anything else until the end of my ride. Using the cadence monitor has improved my pedalling by leaps and bounds while saving my knees, ankles and muscles. When I started monitoring cadence I was at about 76-86, the day I went over 90 I thought I was just too cool. Now I ride between 95-103 pretty much all the time and keep it around 80-85 when climbing. I firmly believe the reason I can ride a century 1 day and 25-50 miles the next is because of my cadence.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"