aacf4497__Blogger__Tumblr_and_Posterous__0
[Blogger.com] Allows import/export via XML format. [Wordpress.com] Allows import from lots of other services and allows XML Export. [Tumblr] No Import/Export Option. Mac users can however backup their blog using an application. [Posterous] Allows Import from Lots of other services. No Export option available. [0] 
Import Export Options
Choosing a Free Blog Host - Comparing WordPress.com, Blogger, Tumblr and Posterous
0