That's true - the Canon cameras unfortunately use the brain-dead PTP (Picture Transfer Protocol) instead of the more sensible USB Mass Storage protocol (except for a few high-end models that have a menu option to switch). I tried the N800 with my Canon camera just to be sure, but as expected it says "no file system". But I guess I can always transfer the SD card or use my USB card reader instead.

I did some testing of USB host mode with some of my other devices, directly connected and with an nGear hub in powered/unpowered mode.

Both my 1 Gbyte Sandisk USB memory stick and my 4 Gbyte OCZ Rally USB memory stick worked fine when directly connected. The card reader did not: the power LED went on when connected, and it appeared to be detected, but as soon as a memory card was inserted the power LED went out and the N800 gave the "unrecognized USB device" and "no file system" errors. Power issue, I assume.

The behaviour with the hub was a bit strange. When the hub is powered from its own power supply, and I connect to the N800, it is detected ("unrecognized USB device" as usual). But the power LED on the hub goes out a second later (huh?). However, it comes back on when a device is connected. That's not normal behaviour, at least not when I use the hub on a PC.

The 1 Gbyte memory stick worked fine on the hub, whether the hub was powered or not. The 4 Gbyte memory stick did not work very well on the hub, whether powered or not - I only got it to be properly recognized once out of 10 tries. The memory card reader did work successfully on the hub when it was powered.

When I say that devices worked, I don't necessarily mean that they were recognized immediately every time while I was plugging and unplugging various devices. Sometimes a device was not recognized on the first try, but unplugging and replugging made it work. I did not reboot the N800 during any of these tests.

I'm not sure how to interpret all that. It seems like the N800 has some issues with the hub that it doesn't with the devices connected directly.