Over the past few weeks I've noticed an annoying behaviour with Blogger. It seems to remove large chunks of your template. A good backup is the remedy. There are some backup programs you can use like BlogCollector or BackupMyBlog to name a few.
Another promising one is HTTrack Website Copier which I am trying out. This program is a free, offline browser utility which downloads your blog to your computer for viewing when you're not connected to the internet. It will copy all web pages, images and reconstruct internal links for offline browsing. I like the fact that you can simply update the backup on your computer.
Another method that I have been using (and will continue to use until I decide to go completely with HTTrack Website Copier) is copy and paste your template into a notepad program, date the entry and save it on your computer. That has been a lifesaver for me. There have been countless numbers of times that my blog was missing large segments of content and I reinstalled the newest backup to correct the problem. Of course, the obvious problem here is how recent is your backup? My suggestion is to do a backup after any major additions to your blog. That will insure that all your work will not be lost in a blogger glich.
While researching this, I came across a couple of interesting articles with information on backups in general, including backing up your hard-drive. An excellent article can be found at Lifehacker, Geek to Live: Automatically back up your hard drive. Ask Lifehacker Readers: Best online backup service? has information from many of their readers. Also, PC World has an article, Store It on the Web. Just remember to read the warning if you decide to go with an online storage system.
The question should not be "Will I do a backup?". The question is "How shall I implement my backup program?".