I've just tested a Hawking HUF11, which is based on the Realtek 8150, and so far things are looking great!
I put the N800 in host mode, plugged the sucker in, brought up the interface and transferred a big file via scp, no problems at all, and no power injection seems to be necessary (phew)
It looks like I'll have to do some more tweaking around though, as at least the web browser tries to bring up the wifi interface, but I don't think that'll be too difficult to fix.
Edit: DUMMY IAP is necessary (thanks rps!!!), run
gconftool -s -t string /system/osso/connectivity/IAP/DEFAULT/type DUMMY
and select DEFAULT from the connection list after bringing up your interface with udhcpd, or whatever.
I have an adapter like that on the way, but for now I'm using a normal male mini usb cable plugged into N800, with the other end, and ethernet adapter plugged into a female to female adapter.
I am very interested in purchasing a USB to ethernet adapter that will work with my N800. I have been searching for the Hawking HUF11 that was mentioned in this thread, but have not found a place to buy it. If anyone knows where this can be purchased or another usb to ethernet adapter based on the Realtek RTL8150 chipset I would be very interested in it. This is one of the main things I want to use my N800 for: configuring routers with a wired connection. I know I can get a portable router, but I would rather go this route if possible. Thanks for any help anyone can give! I have upgraded my N800 to Beta OS2008.