When I don't use my headphones I often put them on my turntables, but when I have records spinning very often I put them on the jog wheels of my CDJ2000nxs.
Some guy told me not to do that because the magnets will damage the CDJ. Being skeptic in nature (and being an engineer as well...) I had a look at the manual and didn't find anything about it. The magnets in normal dynamic DJ headphones are not huge and I doubt that they can damage anything inside a CDJ. I don't know which type of encoder is used by the cdj2000 jogwheekl (optic? magnetic?) but I've never noticed anything funny happening with the headphones laying on the jogwheel, so I suspect that even if the encoder is magnetic the field from the headphones is so weak that doesn't interfere with it.
Any experience/toughts/statement about it? Would be interesting to hear something from Pioneer. There's nothing in the manual so it should not be an issue, but I'm curious :)