Actually interestingly enough full screen apps that have palettes are really nice on multiple monitors. Omnigraffle, etc. The palettes can live on top of the linen on your secondary display. it makes using Keynote, omnigraffle and similar apps such a joy.
That's great, but the whole reason I like multiple monitors (instead of one big one) is to segregate tasks. For example having full-screen terminal on one monitor and a browser on the other.
