Well, you'd better not be thinking what I think you're thinking, because my answer is the same as always — no threesomes unless it's boy-boy-girl. Or Charlize Theron.
[NAFDA] Workshop, post, discuss, and read Smallville fanfic here. Most, but not all, will be slashy. After all, PPO does stand for Pansexual Prettyboy Orgy.