[caoimhin]

On a certain level they would be right to complain. Tarsnap has a flaw: buses.

The problem is that Tarsnap is one person. If Colin dies suddenly (in the sysadmin world, the primary cause of theoretical death is buses), you have a problem. Say your account is down to €10 and you have 100G of data stored in there when when the #10 express mows down Colin. You might not be able to get it back since you can't top up your account now unless your method of payment is fully automated on his side.

Looking over his website, I don't see if there is a Colin-backup plan anywhere. There should be. Until then Tarsnap should be one of your backup systems - not the only one.