What can't you do on dual monitors. Once you get used to them you will ask yourself why you waited so long to get the second one.
My main design program, Corel, is always open on the Left 22 and Outlook and IE are always open on the right 19. If I am going back and forth between Corel Draw and Photopaint they are each on a seperate monitor. You can drag and drop files from Exporer into you design programs... It all depends on how you work and what your doing.
At home I have 2 22s and a 19 and I can fill them up in a heartbeat.