I am using gnome-shell with the "/apps/metacity/general/focus_mode" key set to "sloppy".

Steps to reproduce:
- Set the gconf key "/apps/metacity/general/focus_mode" to "sloppy" (you might
  need to restart gnome-shell or log out and back in to make this setting take
  effect, I'm not sure)
- open (say) a browser and a terminal window side-by-side.
- move the mouse into the browser window, giving it the keyboard focus.
- Hold down Alt and tap Tab until "Terminal" is highlighted, then let go of
  Alt.

Expected results:
- Terminal window brought to the front and given keyboard focus.

Actual results:
- Terminal window brought to the front, but keyboard focus stays with the
  window containing the mouse cursor.

If I tinker with the various keybindings in /apps/metacity/global_keybindings
it turns out that the 'cycle_windows' keybinding correctly handles switching
correctly (both bringing to the front and giving keyboard focus). If I set the
<switch_windows_backward" keybinding to something that differs from the
"switch_windows" keybinding by more than just <Shift>, then that keybinding
brings up the traditional Metacity Alt-Tab switcher, which also handles
switching correctly. The "AlternateTab" gnome-shell extension behaves just like
the regular gnome-shell switcher in this regard, so it's not just a 'focussing
windows' vs. 'focussing apps' issue.