I picked up a Nokia 770 out of curiosity. Aside from some obvious and annoying quirks (which probably have been corrected in newer models) it's a pretty neat device. The 770 like the N800, and N810 has USB host mode, with the added limitation that it can't supply power to USB devices connected to it. So I set out to build a battery box that does just that. The box contains a 1000mAH Li-Ion battery, the 5v Boost Converter I built previously, and picoChg v2, which is a redesign of my PCB for the Linear LTC4054-4.2 Single Cell Li-Ion charger IC. The video shows it working with a USB keyboard. The charger is a bit quirky, I might just need a bigger capacitor for it, but it could be the switch I have installed (selectable: ON or OFF/Charge). It charges like it's supposed to but it doesn't always turn the charging status led off when it's finished. Otherwise it works fine. I probably will end up selling the device. Sometimes I get the feeling that I buy stuff because of their inherent limitations, and potential. Once they work like they're supposed to, they're not as interesting anymore.
Just a small factoid for anyone working on USB host mode for this device. Something that I didn't really see mentioned on forums. You need to feed 5V into the 770. Some people on forums actually say the opposite, but it just plain needs it, otherwise it won't notice anything plugged into it :) I wasted some time figuring this out.