Interruptible disk usage tallies for users?

I want to obtain, for every one of my system's users (or at least, every one with a home directory under /home), the amount of disk space their files use. I have root access, but - there are many users with lots and lots of files, and the directory is an nfs-mount. So, counting is kind of slow; and my machine may be rebooted in the process, so I need to be able to resume counting after the machine is up again. What would be a decent way of achieving this? I don't very much mind the output format. Notes: * I can't set quotas. I mean, I have root access, but I don't get to do what I want.