I'd say my public facing servers are under constant attack of some level of utility.
Ie. my honeypot email servers collect 100k+ connections a day each,
that don't have any MX pointing to them, their only sin is being up and
listening to port 25. They can't process a single email in or out.
...the way I know to check if my DNS, SSH, or SMTP daemons have died and need
to be restarted is if the steady stream of syslog messages from probes suddenly
goes quiet.
I thought it was rather nice of the Internet to provide 24/7 distributed service
availability monitoring for me. No more having to pay Keynote to poke my
ports every 15 minutes! ;)
Matt