I ran across a blog today whose author had lost her entire blog due to a problem upgrading to the latest version of Wordpress.
That's a sick feeling, even when it isn't happening to you, the idea that someone's hard work has gone up in smoke. Luckily, she was able to recover from a recent backup and pull the rest of the more recent content from Google's cache.
I can imagine that this would kill many blogs if the content weren't recoverable. It's enough work writing content the first time, let alone rewriting it!
I've just installed the wp-db-backup plugin on my blog. It's available at
Il Filosofo » WordPress Database Backup
By default it doesn't do any scheduled backups, but you can set it to email you backups on an daily or weekly basis (hourly, too, but I'm not that obsessive yet).
Jay