Hi JavaFan, thanks for your answer.
We do have deployment software, I just don't trust it much :) I don't know if there's a policy on 64 bit software, but the pattern tends to be, "if the 64 bit version offers important advantages, we install it, otherwise not". Eg databases or large application software is almost always matched to the hardware, but we also have a suite of about 50 32 bit command-line tools which are available and used on all machines.
So I guess you've helped me refine part of my question to: "are there important advantages in installing 64 bit perl on 64 bit windows?" I have not yet come across any.