Thanks for your answers!
Nope. Works fine. Between the nightly hot-copy backups and the internal design of the SVN FSFS storage engine, I'm not terribly worried.
I tend to use svnadmin dump for my daily backups. (some time ago, I ran into compatibility issues with hotcopy when trying to restore on a different OS and it kind of frightened me.)
What would make you prefer to use hotcopy rather than dump? Performance?
(We took advantage of repository sharding in 1.6, which is why we did a svn dump/load method. If we didn't need sharding, we probably could've just copied the directory tree across from the 1.4 to the 1.6 server.)
Did you consider the type of filesystem when setting up sharding? Or would you consider ext3 as good enough?