Just for fun I looked up 4:20 on Wikipedia, here's the link:

http://en.wikipedia.org/wiki/4:20

Oh yeah, I've heard just about all the urban legends about 4:20, although the Abbie Hoffman one is new to me, but the only story I have heard or read about repeatedly in print is that it was the high school kids. Anyways, fun little urban lore.

Peace