When an NFS server machine is using an ext2 filesystem with quotas enabled,
and has the filesystem exported via NFS to a client machine, and the client
machine creates a file then chown()'s it to another user, quotas do not get
correctly updated on the server.  I have tested this with a stock RedHat
6.1 server and client combination.

For example, on a server, create an ext2 filesystem and a directory
/export.  Setup and enable quotas on /export.  Export /export to a client.
On the client, mount /export.  On the client, create a large file owned by
root in the mounted filesystem.  Then chown() it to another user.  The file
will still count against root's quota as far as the server machine's quotas
are concerned.