DFU mode "disabled" by OSX 10.5.6 update

Some tips from the iPhone Dev Team on how to overcome this issue:

DFU Issues in OS X 10.5.6

Lots of users have been experiencing problems with the use of DFU mode after applying yesterday’s 10.5.6 system update.

We believe this behavior is due to a kernel bug not a specific countermeasure by Apple. Possible fixes are (try at your own risk!) -

1. Replace the following plugin kexts from within IOUSBFamily.kext with the ones from 10.5.5 and then rebuild kextcache (if you don’t understand this, then you shouldn’t attempt it!)

/System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/AppleUSBHub.kext

/System/Library/Extensions/IOUSBFamily.kext/Contents/PlugIns/IOUSBCompositeDriver.kext

2. Use a USB hub in-between the DFU device and the Mac and insert/reinsert the iPhone’s USB cable.

3. Use a PwnageTool created .ipsw on Windows! Oh the irony!