I only encountered fanfic three years ago, but never before have I met Mary Sue in her full and frightening glory. I now have, thanks to pinkdormouse who provided a link to agentsands where the story was posted; she was also kind enough to give the author some constructive criticism. The post might disappear as the mod threatens to delete it unless it's put behind a cut, so here's a snippet to preserve the best of it.
[She] gazed into the mirror. A tall and slim, yet with beautiful curves, 22 year old woman gazed back. With long, ebony, blue-black hair down to her waist, smooth skin as pale as ivory and as flawless as a porcelain dolls, a heart-shaped face with high, well-defined cheekbones and pale pink lips the shade of a rose frozen in ice, with well-shaped eyebrows, a nose that women who had nose jobs would kill for and a swan-like neck Nicoletta could easily have been a model or an actress, but, it in her eyes where her true nature showed. Framed by long and curling coal-black lashes they were the most beautiful, and terrifying thing about Nicoletta. The whites were like opals or pearls and the blacks like black diamonds but it was the irises that were the part that captured people. Irises, deep blue like a sapphire, but gentler than that, like a mountain pool where a star had fallen from the sky to land in the pool and to sparkle and twinkle in its depths. With pure silver outlining the irises and pupils they were like witches eyes. Some people found them beautiful, others, terrifying. Nicoletta didn’t know whether she had got them from her parents, or, what seemed to her as more likely, she was the only person in the world with eyes like hers.Sigh. Absolutely magnificent. I can cross off one of my fannish ambitions now.
[Edit] pinkdormouse wrote an answering parody in which she kills the Mary Sue using one of her own characters, the wonderful Marianne.