I too do pilates, and the bellybutton to the spine thing, to me, is isolating the abs and not so much about "sucking" as that (to me) implies using your diaphragm (i.e. sucking in your breath?) but of physically pushing your stomach muscles down using your core muscles. If I do it right it puts into play all the abs, the butt, and the lower back.
I drink a couple cups of coffee with milk in the morning, but there's no way I could do pilates after eating solid food.
And just as an aside, I could not possibly do pilates any slower than Winsor - I like Dummies because if anything, she moves things along a little bit faster. I do each movement with as much control as possible, but I've started doing it much like I do weight lifting. Concentrating on feeling each muscle working and pushing it as hard as I can, striving for correct form. This is probably why I have never succeeded at Yoga. I'm far too impatient.
I have found that using a mat has helped a LOT. You don't say how long you've been doing pilates, but I've been doing it now for a relatively short period of time, about 2.5 months. It has increased definition, length and strength in my lower body to the point where my tendons no longer hurt when I run, and now it's my wind which lacks, not my muscles. It has increased my ability to handle my lower body workouts with weights, as well.
