Ten days before a photo trip to Europe, the shutter failed to operate properly. Canon could not promise me that they could fix the problem and return the camera before I left on my trip.
Ironic - my 1Dsmk2 had the shutter die with about 11K actuations about 10 days before a trip this last January.
I ended up purchasing a 5D as a backup and have been happy with it.
With the likely release of a 1Dsmk2 successor this Fall, your camera's value will likely lose its value more quickly than if the new version were not being released.
If a 1Dmk2N or 5D could adquately serve as a backup this route might make better financial sense.
Or if you don't regularly need a backup (for example paid work, weddings, etc) and will have access to cities/stores another option is to not have a backup, but just rent one when needed, or buy one and then sell it used when the primary is repaired.
As others have said, if you *need* to get the shot than you need a backup, but if having a replacement camera tomorrow is an option, than you might go with one of the other routes above.