Webhost "Peachy Dandy" disappears... with my sites
Note that they appeared perfectly legitimate: reselling on behalf of a reputable firm [Hawk Host], offering a normal range of hosting plans from a few dollars a month to $80 or so. They had hosted these two domains for 18 months without any significant downtime, and had responded quickly to my (few) support tickets over that time period.
Neither domain hosted mission-critical services, just a company blog and web-facing marketing material. The MX records pointed to another mailserver provider. Therefore I had no automated monitoring pointed at either domain, and did not immediately realize that the servers had gone down. (My focus was elsewhere; I first found out when I casually attempted to login to Wordpress later in the week.) As a consequence, I lost these web presences for days, and undoubtedly lost company email [as senders could not retrieve the MX records from the nonexistent nameservers].
tl;dr moral: Monitor EVERYTHING. What happens if one of YOUR hosting vendors silently evaporates while YOU'RE focusing elsewhere? Write out the entire chain of dependencies for your email domains, web domains, DNS redirects, IP forwarding, etc. Do this again every few months. If a host/service really isn't mission-critical and you therefore don't want to pay for third-party monitoring, at least setup cron jobs such that your hosts/domains cross-check each other at regular intervals. Remember: Your 1337 skill set is useless if you are not aware of priority issues. Don't let what should be just an hour or two of email/www downtime balloon into a serious impact on your brand.