First of all, a tiny miracle. This morning when I went down the stairs for coffee (I live in a really really stupid stupid split level) my knees did not hurt. Usually, I have to hang onto the banister and hobble down the stairs one at a time (two feet per stair) like a very old lady. Today I just walked down them. A result of exercising? I don't know. But I had less knee pain today than I usually do. Other muscles made up for it, however.
For example, my quadraceps hurt all day (more stairs...stupid split level...grumble, grumble) but it was a good kind of pain. The kind that reminds you have muscles where before you thought there was only 20 pounds of marshmallow fluff. I had a busy day (as usual) and didn't do my second day's workout until late (10 pm). Of course I did Level 1 again (indeed, it will be some weeks before I can follow anyone on the Level 1 workout other than the demo girl who does the very basic "beginner" moves, like ladies' pushups and that sort of thing). Once more, I could not get all the way through the workout without stopping to rest occasionally...legs just hurt too much to complete the cardio circuits. But I think I made it further in before running out of steam. And I noticed a slight improvement from last night in balance and flexibility.
The very very hardest part is going to be sticking with it every day.