It's 2012 and X servers still haven't solved the Alt / Meta debacle. Somewhere between the NX client on Windows, its X server (a version of Cygwin) (or, on the Mac, OpenNX / XQuartz), the NeatX server on Linux, and KDE / Gnome, things get messed up and keyboard shortcuts don't work. New rule: Alt and Meta are the same. Always.
Hmm. This is a bad rule when you actually have both an Alt and a Meta (Windows or Command) key, though. - Victor Ganata
F* this. Make your Windows key Mode_switch and use it for accented characters only. - Tudor Bosman
Except lots of apps have defaulted to keeping Meta and Alt separate. This is why I suspect no one has ever tried to "fix" it. - Victor Ganata
KDE tries to fix it by handling Alt and Meta the same (it doesn't do it very well, not in KDE 3, anyway). Gnome 3 tries to fix it (but it's Gnome 3, which sucks in many other ways). Emacs doesn't use Alt shortcuts by default (despite the backronym). I believe Firefox tries to keep Alt and Meta the same. It sucks that this conversion is done at the application level, and each application does its own slightly buggy version of it. xmodmap makes things more complicated (doesn't it always?) -- different applications detect keycodes, keysyms, or modifiers, and xmodmap can modify all mappings between them. - Tudor Bosman
I separately bind alt and meta in my emacs. One gets OS conventions and one gets emacs conventions. But I generally agree that the alt vs meta thing is broken. - Amit Patel