I'm not worried
most will be a recompile - a few things will require work to be 64 bit clean. I think the move to Perl 5.8 from 5.6 was more disruptive than this will be.
"Whenever you find you are on the side of the majority, it is time to pause and reflect" --Mark Twain
"The significant problems we face cannot be solved at the same level of thinking we were at when we created them." --Albert Einstein
"This is still a dangerous world. It's a world of madmen and uncertainty and potential mental losses." --George W. Bush