But that's no use if you use the default TTL of 2-3 hours that I always see whenever I configure new dns entries. Sensible TTL should be at least 24-48 hours, maybe even more for your returning users to not be affected by those kind of outages.
A 24-48 hour TTL means you're hosed for 24-48 hours if your hosting service has an extended outage because you can't point any of those visitors at the IP addreses at another host. With a short TTL on the other hand, the worst-case scenario is that your DNS provider is offline and you have to change nameservers at the registrar. With a hosting outage, you can just point the domains at the new IPs and be back up in minutes to hours.
