Sooo ... does anyone do any exercise/fitness training on bikes? I'm really wanting to get into this for a few different reasons. It's something I can get my husband to do with me. My in-laws got us bikes for Christmas last year and we've hardly used them.

And my husband has decided he wants to enter a 30 mile ride for MS in late September.

Sheesh!
So, does anyone ride? Mountain bike, street rider, etc? Do you find it effective? Are there ways to spice up the routine?
I want to alternate bike training with the C25K stuff as well as doing some toning with JM:30DS/Fitness Ultimatium.