Sometimes I'd like to switch between windows using Alt-Tab or similar shortcut without the popup (showing window thumbnails). Is it possible in 12.04? Thanks.
A quick look at the CompizConfig Settings Manager (CCSM) suggests this is not possible for the default Unity switcher. I don't see any settings there related to time-out, so I'm afraid the simple answer is "no", unless someone can tell you about hidden settings somewhere.
What you could do is switch to an alternative switcher. In CCSM you can disable the Unity switcher and replace it with e.g. the
Just keep in mind that this alternative switcher doesn't look as pretty as the default switcher. However, it does offer a wealth of other functions (for example, this one allows you to click the window you want to switch to). Also remember that CCSM can be a dangerous programme and might break Compiz if you select the wrong window.
If you want I could upload a screenshot, just let me know :)