My rollers arrived today, so I set 'em up and had a go this afternoon...
It took a few minutes to get the hang of it. It feels like a bloody long way from the ground!
Anyway, I set them up in a doorway with some cardboard underneath to protect the floor. I wobbled a bit to start with, but the answer seems to be speed. I gradually got steadier, and the wobbles came less frequentley, but they still came. This, I'm sure, will get easier with practice. The hardest part is getting on and off! (Well, more "on" really.)
I did 10 miles on them, and sweated like a fat bloke shovelling coal. I had to get off to find a solution, and ended tying a rag round my head, Japanese Kamekaze style, which seemed to do the trick.