You should have the choice of 1 or multiple... especially if the monitors have different resolutions.

Like my Dell Mini9 (1024x600) and my SyncMaster 216BW (1680x1050).

Very disparate screens and tough to make them feel right. only way I could get it possibly look right... Dell Mini9 normal, Syncmaster rotated 90 degrees. but it wouldn't do that for long before it reverted automagically.

Yeah, I know.