lorax - 2:39 pm on Nov 2, 2013 (gmt 0)
Backing up is always a good idea. I think an automated back up before update could easily be done and likely we'll see it as added feature to one of the several backup plugins already avaiable.
But if you don't mess with the core code, use child themes (as WP strongly encourages) instead of editing the parent theme directly, and stay with approved plugins (those on the WP site) that still have support and updates you aren't likely to run into any trouble. I've built hundreds of WP sites and manage nearly 60 install of WordPress from small sites to large multisite networks today. I've been using WordPress for clients and my own sites for over 7 years and I've never, NEVER, had an upgrade go wrong. Just sayin - the updater is a pretty solid tool.