mni was a superhero RPG character I played in highschool.
He was pretty much good at most things, thus the name. That and he was tech oriented (sort of an Iron Man type) and it sounded good and techie.
When it came time to sign up for my login, I was told that geeks were variously into computers, gaming, science fiction, realscience, anime, SCA, and possibly even parties. Since I'm into all of those things, the name came to mind.
Plus, it sounds cool.
Funny story wise, I was actually the second omni@b. Some other guy had it in 1986. The only way I knew this was that a few weeks after getting online, I got a talk request from a girl I didn't know. Not that unusual, that, so I chatted at her and answered her questions about how my summer was. It was awhile into it that I figured out she thought I was someone else. So I decided to lead her on from that point, and suceeded for quite awhile. Luckily she took it well when I revealed the ruse. And Thayer and I then became pretty good friends. She was the about the only person who knew the other omni, who's name was Brian as I recall.