In college, to research direct mail marketing for a paper, I subscribed to a bunch of magazines using a different middle initial for each one. When the junk mail started pouring in, I traced each one to the magazine list they must have gotten to reach me. Some of it made good sense, but why a person living in Southern California who subscribed to Popular Photography got catalogs for crop seeds was weird. Got an A by the way.
When email came out, I followed suit. I signed up everywhere as 'just another dude'. To this day I get email, "Dear Justin..." It all gets filtered into a folder called Justin. Some of it's funny, but how all these people found out I need foreign Viagra is a mystery.