'ctrl-pgup'/'ctrl-pgdown' - when switching browser tab the content page also switches.
scrollwheel doesn't advance to next page
can't select text for copy / paste.
on a small resolution the right hand side doesn't scroll with main content.
middle click doesn't open a new tab (if the mouse doesn't have middle button, the scroll wheel often is clickable and performs the middle click). In same vein, ctrl-click doesn't work (I think in IE world, shift-click also is used to open in a new window).
search for text is broken. For example: on the opened up starwars page I want to search for 'Boba Fett'. I press ctrl-f, type in 'Boba fett', and I get nothing.
I do miss the buttons for: edit/view history/view discussion/other languages. I don't need new functionality behind the buttons, just a way to see them, they can be linking to the real wikipedia for that.