Interestingly the Wikipedia entry says you shouldn't. They also say LiIon batteries die pretty quickly if they get too warm - say in the back of your N800 attached to the dashboard of your car on a sunny day. Apple say similar things about their batteries. NimH and NiCd batteries are the ones that need deep cycling. Then again, I've yet to own a mobile device whose battery hasn't totally given up within a year anyway (my laptop's battery is totally dead, it doesn't hold charge overnight any more). So I don't think it really matters