Reader Jake Tesler just can't leave well enough alone in regard to a Lion "feature." He writes:--
In Lion can I display multiple full-screen applications at the same time using more than one monitor?
I'm not sure why you'd want to see the inside of a can of worms--honestly, it's quite unpleasant--but as you insist, let me crack this one open.
No. You can't.
Lion's implementation of full-screen applications--even in multi-monitor configurations--is to dominate your displays. For those applications that support it, you can run an application in full screen on one monitor and move windows within that application (tool palettes, for example) to a second monitor, but you can't run Full Screen Application A on Monitor 1 and Full Screen Application B on Monitor 2. Rather, what Apple expects is for you to use Mission Control and swipe between the two.
And yes, I understand that this makes some people unhappy (as the comments below will undoubtedly bear out).
The workaround is to resize the window of each application (try clicking the Green resize button in the menu bar) so that it consumes the screen without going into the official full-screen mode.