I don't' have the camera so I haven't read everything about it...but I have read quite a bit. Apparently, it's easy to do and it's easy to change back to the original firmware at any time. It's not physically changing anything...just the soft ware that runs the camera. I've read that it's actually a DOS based software.
I've heard a lot of people who were concerned about the warrenty...well, if you do ever send it in, you can reset the firmware. Although, I've heard that people have sent in hacked cameras with no repercussions.
Maybe take a short walk over to the zoo that is photo.net as read up on all the folks who have installed the hack.