William Safire blogs the word "blog" in his On Language column today.  He specifically mentions xanga.com --

"Blog is a shortening of Web log. It is a Web site belonging to some average but opinionated Joe or Josie who keeps what used to be called a ''commonplace book'' -- a collection of clippings, musings and other things like journal entries that strike one's fancy or titillate one's curiosity.... To set one up (which I have not done because I don't want anyone to know what I think), you log on to a free service like blogger.com or xanga.com, fill out a form and let it create a Web site for you. Then you follow the instructions...."