*Known longest overall, from the heyday of paper 'zines:
astrogirl2 . Damn, woman, it's been around 20 years now, off and on, hasn't it? We've killed a lotta trees between us.
*Known longest in RL:
countessaleska . Damn, woman, it's been nearly 15 years. Lotta water under the bridge (and in the basement). :P ;)
*Known longest, having met in a strictly online context (if I'm remembering/reading profiles correctly):
laws_of_fizzix. Damn, woman, it's been . . . what, about 3 years? Well, okay, anticlimax after the others. But they've been a good three years. And they're *internet* years, which, given how fast the 'Net moves, are probably like dog years or something . . . ;)