Clearly any good lens maintains it's value for years. I just sold my nikkor 640 with a profit after using it for 2 years.
On the other hand, I don't seem to be able to unload my old D300 at $300. That was a $1800 camera body. I saw the like of D3x selling at $2500 from the original $8000 price tag. Looks like buying new bodies are really wasteful.