i use them as chain stay protectors. cut to fit and cut them lengthwise, wrap it around your chain stay, and then put as many (or few) zip ties as you want. a lot cheaper than a "lizardskin" type protector, and they keep your frame from getting all dinged up. i also have pieces zip tied on my bike rack, where the derailleur rubs (or would rub, without the tube piece).
i also use them as little gaskets for my water bottle cages, so they don't scratch my frame.