LAST EDITED ON 05-21-03 AT 00:08 AM (EDT)
 
Edited for spelling

Lemme be the one to put the last nail in the coffin here...
Oh, and Gryphon, apologies in advance for the Trek references. I'm quoting here.

"Mary Sue" Story (fan/fanzine): A story in a fanzine that deals with the adventures of a perfect heroine, who is obviously the author as she would like to be(almost all such stories are written by women). The term derives from a story submitted to the fanzine Menagerie. The editor, Paula Smith, could not in good conscience print the story, but proceded to write and print a parady, using the name Mary Sue for the heroine.
Mary Sue is the youngest, smartest, most beautiful ensign on board the USS Enterprise. She outwits Klingons, seduces Mr. Spock, reinvents the Warp Drive, ad infinitum, ad nauseum. In short, Mary Sue has become the symbol of the perfect heroine, and when she appears in profesional fiction, editors recognize her and insist that she be given a few flaws to make her more human, whether she is or not. (There have been a few Vulcan Mary Sue characters, too.) Mary Sue has a male counterpart, "Marty Su," who is just as obnoxious.

-Futurespeak - A Fan's Guide to The Language of Science Fiction by Roberta Rogow

Hope this helps.

-NeoRaven