Not all wifi dongles work with the RasPi. I've had good success with this unit:  http://www.adafruit.com/products/814. I'm running 15 Block Erupters on a RasPi with this dongle. I'm assuming that your wifi dongle is on one of the hubs, not on one of the RasPi USB ports. Some dongles draw more power than the RasPi ports can provide. Also, six Block Erupters will use all of the power on a D-Link H7 hub, so your keyboard and wifi dongle would need to go on your 4th hub.

The easy way is to use a wifi bridge or game adapter that you connect with an ethernet cable to the RasPi ethernet port. If you can get the bridge configured correctly (which you can do on a PC), then it's just about guaranteed to work with the RasPi. This also saves a precious USB port.

-R8