I have the D70. After this week, I expect to use my D700 almost exclusively. But I have no intention of selling my D70 for some modest amount. It still outperforms any point and shoot on the market.
I plan to keep the 18-135 lens mounted on my D70 (almost permanently) and use it more like the family point and shoot. I'll let my wife use it - she has been otherwise forbidden from touching my camera equipment . I think I'll hang it over my shoulder for longer, more rugged, unprotected walking around use (like on the beach) than I did before. I used to baby it more and always keep it gently cradled in a camera case.
This may certainly be the case until Nikon comes out with the FX equivilent of the 18-200 VR lens for travel, etc.
Maybe I'm wrong. Maybe once I get a D700, with it's huge view finder, huge LCD and better image quality, I will never want to pick up my D70 again. But I hope that the D70 continues to serve some duty in my family for some time to come, even if it takes its place in the back seat. I would hate to see my loyal little D70 become a forgotten soldier.