I'm being really optimistic. I think reason 7 is something really cutting-edge. Like FULL support for a 3 button mouse? Or... gasp... one of the newfangled mice with a scroll wheel? 

Just imagine being able to scroll in the Heirarchy editor..., or zoom with the wheel.
Just imagine right-clicking on a figure and having meaninful stuff pop up in a context menu. Stuff like "Turn off IK". I shouldn't be ungrateful, I guess we do currently have "Toon Tones" and "SreeD" right there at our fingertips in one of P6's only context menu... very handy.... anyone ever used 'em?

I'm all for backward compatibility, and I know there are still folk out there who uses a one button mouse (pushing it with both hands, no doubt), but I think it's time they entered the new milennium. A 3-button mouse with a scrollwheel costs around 10 bucks.