I've use a book, a towel, the lid off the primary, a stack of CD cases... whatever's handy. It kinda amazes me they SELL something to do this. But then again, not really.
Sorry for not being more specific. I only use them for racking as Turock stated. I have found them to be a less costly alternative to the ones sold at the LHBS.
GTS
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Often wrong, but never in doubt!
I keep all mine that way until they stop dropping sediment. If doesn't matter if racking or not. The purpose is to keep the sediment lower at one side of the carboy. I use a long enough piece of wood that the carboy doesn't rock. I haven't come close to knocking one over or moving it at all.