When my Polar S720i HRM died on me, and I was forced to train without staring at numbers and trying to hit certain heart zones, I actually started to enjoy riding my bike more. I'd go out and train and just hit hill after hill, not caring if I was pushing my HR up more than I was "supposed to," and as a result, I've become a faster rider.
Not to say I don't want a PowerTap, because I really do, it's just that sometimes it's not a bad thing to ride without thinking about numbers.