Thanks for the comments on our Tumblr Backup. Right now we're focusing on one-time backup but will quickly be offering daily/weekly backups not much later.
Yes - we can do this yourself. There's people that feel comfortable doing that but there's many more that don't.
As for Tumblr providing a backup solution, yes they have but it (1) doesn't usually work, (2) only works on a Mac, and (3) still in beta, (4) hasn't been updated since 2009, etc...
@mootothemax - we'll work on providing more details on the site here soon. Thanks for asking for that.
@ZackOfAllTrades - like the idea of providing an automatic site up if/when Tumblr goes down.