I use blogger. No easy way to backup the content so I subscribe to my own blog. Of course if I had to rebuild, it would be a royal PITA. But at least I've got the contents.
If you are using seperate domain for your blog then you can take backup of your mysql DB through cpanel (backup option). If you are using WP for your blog then there is WPbackup plugin available which takes backup itself (daily,weekly or monthly) whenever you want. DON.
People, people, people. Nivedita has a blogspot hosted blog. You cannot back it up. With Blogspot, not sure if you really have a need to worry about it. I have not heard of anyone losing their blog data yet. I am sure they have it well taken care of.
I think this is the way to do it for blogspot blogs: Dashboard > Layout > Edit HTML > click Download Full Template. To upload it again, the space is just below the "Download Full Template" box. Hope I made it correct. Good luck!
login to your blogger account... then point your browser to.. http://draft.blogger.com.. select settings for your blog.. select export.. select export again.. save .xml file. Will save your content and comments (i think comments as well)