automated package upgrades

[Jeff Weber]

What is the current wisdom regarding automated package upgrades, especially
when kernel upgrades occur?

Say I enable automated daily upgrades via a cron job, e.g.
    smart upgrade --update

which then in turn upgrades the kernel.  Will the system then be "unstable"
until I manually reboot?  (I recall other systems that advise rebooting soon
after upgrading the kernel.) If so, are there recommendations for how to handle
kernel upgrades when smart is configured to upgrade packages via cron?

    TIA,
    Jeff