I wish I could have "soft" desktops/displays on my Mac.
That is, I'd like the second (or third or more?) desktop to display to a VNC server while still maintaining the hardware LCD screen as an independent desktop. Then, I could open a VNC client on my work machine and move some windows over there. I can do this under Linux with some X11/VNC tomfoolery, so I miss it--though I do understand how and why Quartz != X11.
I've noticed that the green maximize button in Tiger windows does the thing I expect more often now. That is, it makes a window alternately fill the screen (except the dock) or shrink back to the size before I hit the button.