This is guide compromised of information documented by myself, Beta, Bibin, Ashen, and a few others. I'm putting the information I find useful all in one thread for convenience and ease of use.
flax MSPaint Illustrations! Yeah!REV3-4
Be sure to pull off the extra capacitors before you start cutting, and don't cut the lines exactly like I drew them. Cut a little bit in front of the line and then sand it to the exact size you want. You break less boards this way. The blue lines on the back are 3.3v traces you need to relocate. Also, my label for 3.3v didn't show up very well, but it's where the yellow dot it is. Let me know if there's any issues. I do really suggest trimming a bit more conservative near the AV chips. Depending on how close you cut you may need to reconnect the traces infront of the expansion slot on both sides of the board, but that should be obvious.
If the trim isn't working, try this fix courtesy of ßeta/Ashen in which a 2k resistor is connected to PIF 8 and 3.3v.
So, I got the board I posted previously working through some trial and error on another board. ( I haven't thoroughly looked through Beta's diagram yet, he may already have noted this.)
Ends up, all it was is a 2k pull up resistor on pin 8 of the PIF that connects to 3.3v. ;)
PIF pin 8 --> 2k resistor --> 3.3v
You can trim the higher revisions in the same fashion, but the chip pinout for audio and video are different.
Pin 17 Right Audio
Pin 20 Left Audio
Pin 27 Composite
I couldn't find a great picture of the chip so this'll have to do.
If the trim isn't working try the resistor fix discussed above.
If you want to remove the portion of the board with the U8 chip on it, you'll need to cut it off and bridge pins of the PIF to get the board and controllers working again.
I'll update this as I find more useful information to add. Thanks to everyone that contributed.