Using Robocopy from the resource kit. We have a backup server in another building. We robocopy the files from two other servers to this one every night, just after backing up that server. This speeds up restores, 90+% of which are from the day before (just copy it back), plus, since robocopy can copy security information too, if we have a file server crash all I have to do is change one line in the login script and the users are pointed to the backup server (with yesterday's data, of course).
Robocopy has another advantage over copy or xcopy in that it can also remove files on the target, to make a true mirror image.
I think once we go to active directory that there will be better/easier solutions for this, but for now it works great.