rsync taking a while on really large files

[David Trammell]

Can anyone suggest a good way to speed up rsync on really large files?  In 
particular, when I rsync the mail spool directory, I have a few users with 
inboxes over 1GB and up and it seems to take a very long time to just 
compare the files.  Maybe it would be faster to copy from scratch for files 
over a certain size or something if the time stamps don't match.

David