I voted no. I own a 5D Mark II and an original 5D at the moment. I put a hold on a 1DX using my CPS membership so I could get priority, but I didn't put any money down. However, even if a 1DX wasn't in the pipeline I wouldn't put a pre-order on a new 5D because my present 5Ds are doing what I need them to do. That would be different if I didn't have a full frame camera already... or if all I had was an original 5D.
A few thoughts about pre-orders: shop around, especially if you are a CPS member. While you can't get the exact pricing you can certainly ask about cancellation policies and price matching policies. In my case I found a retailer willing to prioritize me as a CPS member and wouldn't charge me until a 1DX was ready to ship. So the risk is 0.
Look, any store taking your money now is being a bit irresponsible in my mind. They can't be sure of when the 1DX is really going to be released, how many they expect to receive and also if Canon will release something in the meantime that might interest you more then a 1DX... like a new 5D. On the other hand, if they create a list of names that have asked to be prioritized, all they need to do when they receive a shipment is call the folks on that list, take their money and ship.
Yes, its true that it is in the store's best interest to take a deposit first (its a free loan!) and not refund it if you change your mind, but doesn't that anger you as a consumer? Hit them back and go to the retailers that don't do this! Believe me, they exist! Call the stores. In Canada Henry's is a good bet.