DisplayLink over USB 2.0 has limited quality. These monitors cannot be used for hi-def video playback and even standard def video struggles unless you have a completely empty usb bus. Once the USB 3.0 displaylink monitors come out then you can truly use them as replacement monitors.
As far as resume/hibernation support....not a problem.
No..no option to feed external power.....and truthfully you really don't need to. These monitors don't need more then 400mA for a 400nit LED-backlit screen...500mA is plenty.
Thats a lot more then just "adding usb ports to video cards"...it has to do with using GPU acceleration routed directly to a usb stream. Aka blu-ray playback and gaming on compatible monitors and no more CPU load.