I came up with my handle when I started writing fanfic in the Buffyverse. Giles was my favorite character, and I turned out to have something of a talent for erotica. I didn't want to put out something so unrepentantly filthy as my first fic under my real name, so I decided to start with 'Giles' and see what sounded good with it. When I thought of 'woman' it just sounded right; saucy, a bit naughty, but with my tongue planted firmly in my cheek.
Somehow it makes me giggle to think that I use a handle I created to protect my private life when I started writing adult-rated fanfiction as my handle on an etiquette board as well...but Gileswench is so much me now that I never think to take another name. I use it on LJ, MySpace, and all my correspondance.