I have been using a hub to back-feed a RasPi. I had to rewire the hub to back-feed. Soldered jumpers between the polyfuse and the uplink port. i also installed a ground wire straight to the connector to help with low voltages. My WordPress server is running on a modified hub and a modified ver1.0 RasPi. This one is hardwired as I had some issues with low TP1/TP2 voltages. Turned out to be loss at the connectors and wire lengths. I recommend a short USB cables for best performance. I had no problems with a ver 2.0 board.
See this post for some more details. It does not show the version 2.0 board version, which is also mounted in a VESA mount with the hub.
http://www.raspberrypi.org/phpBB3/viewt ... 41&t=16473
P.S. this setup powers a HDD and a WiFi with no problem. I also have no problems hot plugging USB devices with either version board. Even the HDD can be hot plugged without causing a reset. Overall stability is better than a RasPi under normal power.