Hey, it's no worse than the depreciation hit you take when you drive that new pickup out the dealer door, Maybe less.
Let's see, I could sell the 500 f/4 and the 1D MK IV and still have only $3–4K to come up with.
Wait... it weighs more than my 500 f/4? In that case, I'll just borrow a 200-400 from CPS when I need it.
I'm also, basically, with those shooters who would be happy a new 100-400 although, the way Canon prices are going, even that lens may break the $4K barrier.
It's a good thing the new 800mm Nikkor is $18K or I'd be worried that Canon is going to pass Nikon for the most expensive lenses. The upcoming new 800mm Canon may, however, continue the skyrocketing Canon lens price trend and take the lead again.