- Check your supplied voltage! Both PSU and cable must be good! http://elinux.org/File:RPI_Test_Points.JPG
- Use powered USB hub
... actually this should be a pre-pre- warning for those companies attempting to power 'miners' off the USB ports.
Current BFL singles don't draw any power from usb so I'm not sure why that would matter. By the way guys, Ben's outlet has the Motorola Droid Bionic Lapdock on sale for $49 today. I picked one up and I'm going to turn my pi into a cheap laptop. While the $499 list price is bull, they usually go for around $60 used so pretty good deal.
http://www.bensoutlet.com/products/motorola-droid-bionic-lapdock