If I'm not able to access and verify my backups, I don't consider it backed up. In theory, this entire VPS is backed up by Gandi, but I'm paranoid enough to do regular backups to my NAS. Same goes for my mail. I have a weeks worth of backups, in 4 hour increments. This not only ensures I get most of my data back if something goes wrong with the server, but it also allows me to undelete something if I realize it happened within that week.
Google does have multiple levels of redundancy for their services like GMail. However, the recent GMail failure for 0.02% of their users did cause them to go all the way to the last line of defense, their tape backups. The real copy along with the hard drive based backups were lost. If you were one of those customers affected, a local backup would have allowed access to messages before Google restored the tape backups.
http://gmailblog.blogspot.com/2011/02/gmail-back-soon-for-everyone.htmlUltimately, the more copies of data you have the better when it comes to disaster recovery. For cloud stuff, I want at least one copy personally, so I can get back up and running if needed on my own schedule.