The first thing I remember reading that could be described as a blog would be John Carmack's .plan file that he frequently updated with his progress on Quake development. This could be retrieved using a dedicated "finger" program, but I seem to remember that mIRC also had the ability.
Excerpt: "The program would supply information such as whether a user is currently logged-on, e-mail address, full name etc. As well as standard user information, finger displays the contents of the .project and .plan files in the user's home directory. Often this file (maintained by the user) contains either useful information about the user's current activities, similar to micro-blogging, or alternatively all manner of humor."
