I turn my pens between centres, usually without bushes. The times I have used bushes, I usually end up with an out-of-round pen, either because the hole in the bush isn't properly centred, or the bush is rocking on my live/dead centre (I don't know which). If I could get a hold of some bushes that were definitely accurate, I would probably use them for rough sizing, then sand and measure the last little bit.
I would probably be interested in trying some accurate bushes which are meant to fit my centres though!
