This has been a scheduled maintenance that's been on the Linode status page (where you should always check if there's an outage) for a week: http://status.linode.com/2010/12/scheduled-network-maintenan...
On the other hand, it is great that Linode had alerts posted on the status blog in advance, and worthy of note that every host will have downtime. Having a backup solution in place should be a responsibility that lies in the hands of the customer, but you're right: without verified notification it's a little hard to plan ahead.
I have to say though, having switched to Linode from a more crowded, oversold host (BurstNET), the difference is amazing.