Here's a patch for something that's been bugging me. This makes Cmd-` cycle through only the current space's windows, which is consistent with other programs on OS X. It also matches the behavior of other-frame on X11 for window managers that implement virtual desktops by mapping and unmapping windows. The patch is attached.
It's not perfect; if you go into Mission Control or so and move a window onto another space without switching spaces, it won't notice until you switch spaces again. I wasn't able to find a notification to listen to; it'd be nice to replace the visible field in a frame with some virtual call that, in Cocoa, would just call out to [win isVisible] and [win isOnActiveSpace], but that'd be a more invasive change. It also doesn't fix the behavior where closing the last window on a space warps you to a window on another space. I'm not sure yet what's causing that.
As far as copyright goes, if this is a large enough change to matter (a decent chunk of the diff is just moving some code around), I'm a Google employee. I'm told we already have an agreement on file with the FSF.
David Benjamin
0001-In-nsterm-update-frame-visibility-on-space-change-an.patch