Back to the original poster, there is also the Moshi Cardette. I have it, it works with most things, USB drives, ipod Touch (charges slower), kind of did okay with a usb hard drive (a new Seagate one). As far as memory cards goes it is fine and the Air should recognize everything. I don't know if connecting the USB ethernet through the Cardette will work, that is the one adapter I don't own. It does run warm when in use but so far it has worked every time.
What do you have plugged in? Are you traveling a lot? How long are you staying plugged in?