It is funny how many implementations of move don't support moving a file across different partitions. First, I wanted to use some of the AppleScripts described in the comments of this hint on macosxhints. But since I use FileVault, my home directory is a disk image, and AppleScript's move will doesn't return an error, but doesn't do anything.
And, I just discovered, that php's rename has the same problem. It looks like versions of php prior to 4.3.3 do not work across different partitions. This is also a problem for move_uploaded_file, but they don't call it out in their documentation.
It seems really strange that these problems are just being fixed now.