Comment 2 for bug 731570

On my tests, the gnome-panel clock is displaying exactly what the system's clock indicates, meaning this is not a problem with the gnome-panel clock, but simply that the computer's internal clock might not be synchronized with that of the other computer you're comparing it to.

You might try synchronizing all your computers to the same time server. On Ubuntu, use this command on a terminal:

sudo ntpdate pool.ntp.org

Make sure to synchronize your other computers to the same time server (pool.ntp.org).

Please report back and let me know if after synchronizing all clocks to an authoritative, reliable time source, they are still running out of sync.