The exception is when I'm watching a movie while having a laptop in my lap.
I can see why it might be handy, say if you want a screen without the menu bar and so forth while doing some photo editing or something, but I don't see it as a huge problem for a desktop computing arrangement.
YMMV, of course. :-)
I wonder why they set it up to behave this way...
Apparently they want you to use "Mission Control" to switch between full screen apps - http://www.macworld....ple_monitors.html
FWIW.
Cheers,
Scott.