[steven]

drfoto, as far as the removing/connecting lenses while the power is on is concerned... I'd imagine that since lenses get their power (for auto focus etc.) from the body, leaving the power on could potentially cause problems.

As for memory cards... if, for instance, you are in the middle of writing/re-writing something (like you are adjusting a photo) and you were to remove the memory card, I believe there is a chance of erasing the data on the card or corrupting the data. As far as I know video game memory cards and even some USB memory sticks also work that way.

Anyhow, interesting thread! It's too bad Nikon US couldn't help you out, but much respect for the thoughtful reply of Nikon JP (and also to Masaegu for relaying that response as well as translating it into English).

I have a D70 and was thinking of getting a D5100 sometime soon.