Potential solution to iPhones bricked following 4.0.1 update
Here's the method:
Download RecBoot 1.0.2
I found it here: http://www.sebby.net/659-released-recboot-1-0-2/
Plug in your iPhone.
Close iTunes.
Run "RecBoot Exit Only"
Click the "Exit Recovery Mode" button.
The screen on the iPhone will go black. At this point, UNPLUG the iPhone (before it starts back up)
It will boot up correctly after finishing the firmware install.
Now plug your iPhone back in and complete a normal restore.
That's it. I spent over 4 hours trying to fix my phone before someone else came up with this solution. Prior to trying this I tried restoring about 20 times. I attempted on both OS X and Windows 7, different USB cables, reinstalled iTunes, and various other solutions people have been suggesting. This one works. Right now my phone's just finishing syncing my music and apps. Good luck!