At work, I use two displays: the internal 17" 1680x105 of the Macbook pro, and a external 20" 1680x1050.
The problem is that the DPIs of each monitor are different: the external has 3" more at the same resolution.
This makes me almost never use the 17" for work stuff, and stuff it mostly with long-lived tasks or log tailing windows.
Now I'm trying something different. I've lowered the resolution of the 17" to 1440x852 (stretched) and that makes the 17" much closer DPI-wyse to the external one, and I can have real work windows there.
Will see how it goes. I don't know if the fuzziness that this stretching causes will make it a very livable experience. Time will tell.
I can only hope that Leopard and its resolution independence will allow me to set both monitors to the same DPI auto-magically.