With the release of Mac OS X 10.6, I think it's time to write down how I use OS X. Perhaps this will be of use to you, or a future me.
On modern widescreen monitors, vertical space is at a premium. Thus, the Dock is on the side. I keep mine on the left for no good reason.
My Dock is arranged somewhat by icon color. Strange, I know. I fiddle with it every so often, but mostly it stays just so.
My Dock, top to bottom:
My Menubar is perhaps the most cluttered place on my machines. I keep a variety of status notification-type thingies up there that inform (sometimes) and distract (mostly).
From left to right: Twitterific, SizeUp, Growl, iSync, iChat, iStat Menus, Spaces, WiFi status, Volume, American flag (the International prefPane), battery indicator, weekday and time.
Clean. Clear. A grey background. I don't want distractions when I switch apps via Exposé. Perhaps I should do something about my Menubar, though...
My laptop is usually, well, in my lap. It's a mid-2007 15" MacBook Pro. Matte screen, of course. I don't often hook it up to an external screen. I prefer to be on the couch or in bed with my laptop than at a desk.
The MacPro at work is attached to the largest monitor I could find (28"). Still, probably not enough.
My ~/Library/Application/TextMate and ~/.emacs.d are full of gold that I drag with me from machine to machine. I am unsure whether I could function effectively without them.