> I get the rationale for avoiding a bottom dock on a widescreen monitor
Depends. I have set my OSX dock to autohide at the bottom, and I'm glad I don't have to move across to reach it. Flick down, boom, Dock. It works even better than it sounds since it works along the edge, not solely where the dock is. Even with multiple monitors, my dock is at most one screen-wide away (even in a triple head setup), while a left-bound dock is two (even three) screenful away.
Also, I seem to unconsciously end up with the pointer in a vertically centered zone. Horizontally it comparatively could stay in any place, left, center or right. Statistically that might be the case too since going up for a (application or status icon) menu will later have me bring the pointer down since I click on a menu entry.
What's more it seems more natural and producing less strain for my eyes to peek up or down than to the far left. Indeed when I want for something to 'disappear' (like the pointer when typing) I move it sideways, never up or down.
Hence since I'm at most a screen width and half a screen height away form the dock, 'flick, boom, Dock' works only at the bottom.
While all of this may apply only to me (and I used a left-bound dock for a while myself, but ended up reverting back to the bottom edge) I understand that some may have other habits and prefer a left-, or right-bound dock. This is why both Gnome 3 and Unity drive me insane, because even if I had a lengthy experiment with a side dock it just doesn't make sense to me, and this is really infuriating to not let people have their way in this case.
(besides, vaguely related to the subject and multi head setups notwithstanding, I find it infuriating in Gnome 3 that the left edge does not reveal the dock and the right edge the workspace switcher. the whole thing just begs for it)