My reason might be too lame to bother mentioning, but since everyone else did, so will I.
My first email account (about 1991, or so?) at a university was assigned to me as:
jgedwa@indiana.edu. From the first letter of my first name, the first letter of my middle name, and the first four letters of my last name. So, since then, I have often used that string as my on-line identity.
jim
__________________
Cross Check Nexus7, IRO Mark V, Trek 620 Nexus7, Karate Monkey half fat, IRO Model 19 fixed, Amp Research B3, Surly 1x1 half fat fixed, and more...
--------------------------
SB forever