There was a huge fuss about the marble madness machine a few years back - I think there was only one in existance and it had not been dumped for use in mame.
So someone from one of the big rom dumping sites managed to track down the owner to see if they could borrow the board to dump the data - the owner said no and he would only sell it for some crazy amount, $20,000 US I think.
Anway, they eventully managed to scrape togehter enough donations to buy the thing but the owner had changed his mind and said he wouldn't sell at any price, he didn't want the game to be dumped.
As far as I am aware it is still not emulated
Will see if I can dig up the story