Hi!
My name is Robin. I've been lurking on KB for months but didn't register until now because I only just had an experience that I need to share with everyone on this board.
I have a Kindle 3 3G + WiFi with firmware 3.1 . I finally took the plunge last week and jailbroke my kindle and installing the screensaver hack. It worked with no problem.
Then today, I installed the font hack. It appeared to brick my kindle.

I tried to connect it back to the computer to load the uninstall file and the computer didn't recognize the kindle. In a panic, I called Customer Service while restarting my kindle and retrying the usb connection. Kindle CS said that yes, I voided my warranty but they could send me an out-of-warranty replacement for $85. Thankfully while I was on the phone the computer recognized my kindle, and the hack uninstall went through, and my kindle unbricked itself and is back to normal.
However, considering that I paid $189 + tax + warranty to a total of $219 at Target when I bought it, $85 for a replacement when I almost broke my kindle doing something that violates Amazon's TOS is extremely gracious and worthy of kudos.