First, make sure you watch the POWERTHIRST video:
If I ride home at a "normal" pace, it's not enough of a workout. So I've been riding home at an "all-out" pace. Since I'm not going to bother trying to do intervals, I started doing fartleks instead (links to the blog I found the term in).
Incidentally, on the subject of fartleks, I asked a genuine Swedish Swede about that and he had to think about the word I just used. He said "I bet we just call it common sense here, just like we call Swedish Massage....Massage."
I've discovered a number of things.
First, I'm starting to go "all-out" for most of my ride, except when I have to stop for traffic and maybe one or two slower breaks to drink.
Second, now that I can see my cyclecomputer, "all-out" means keeping myself above 20mph for over a mile on flat terrain.
Third, I have no choice about getting some cycling shoes and going clipless. With the amount of power I'm pedaling at, the arches of my feet HURT. If we go to Sheldon's guide, that means that I need stiffer soles. I'm, of course, agonizing over which of the many many pedals, pedal systems, and shoes I should go with.
Fourth, if the cassette is just about marginal, I can make it skip under load, even though I can totally ride it when I'm not sprinting.