I have used silicone oil in copiers, and also in printers from time to time.
The up-side to silicone oil is that it's very slippery, has a very high flash point, and is "clean".
The down-sides is that once it gets on something, it stays on it. And bob forbid you ever spill it on a tile floor... broken legs from slipping will result.
I think that what edfair is referring to (white grease) is lithium grease. It's also good for lubing parts, it tends to be "thicker" than silicone oil, and has a high flash point.
The down-side to using lithium grease (or other greases) is that if it's in a dusty area, where toner or paper dust get into it, it can form a "paste" which gums things up worse.
With Inkjet printers, for example, I will clean the bar that the print head assembly moves on VERY well (usually with something like Lexite), then give it a thin coating of lithium grease (also called "reel lube" and can be found in tubes at sporting good stores).
For laser printers, I usually don't have to oil any assemblies, since the introduction of oil into the paper path can be a bad thing.
Of course, anything that you use you should be familiar with; read the MSDS sheets and know about possible interactions with heat, toner, and other foreign objects.
Just my 2¢
"In order to start solving a problem, one must first identify its owner." --Me
--Greg
