10.5.6 = no no DFU mode 🙂
A simple fix for this is to use a powered USB hub.
...or just save your money and use the team dev fix. its really easy.
Thats why you change them back when you're done.
you should already have a usb hub anyways 😛
I have a 7 port hub with 4 usb spots on the laptop itself, and all of them are used(hah!)
If you do have the DFU problem after updating, this tutorial is designed to fix if for you:
http://www.iclarified.com/entry/index.php?enid=2493