Matt I'm sorry to hear about that. It looks like there was a DoS attack targeting another Linode on the host where your Linode resides. We have mitigated this attack now, so you should be good to go again. We apologize for the inconvenience. Please let us know if we can be of further assistance. Good to see my monitoring works, as I saw it straight away, and the host replied to my ticket in less than 5 minutes (y)
Matt No, stopped using Nagios when I reduced the number of servers I have. I've got monitoring setup by the DNS provider, which checks it can access a file every 60 seconds, and also using Pingdom.