I find there is no real reason to have 2 of the same monitor, if anything having 2 different sizes for 2 different purposes works... ofc its a matter of personal taste.
I run 2 different on my home setup, one is a 19" Samsung that runs in 1400x900 that I play FPS on ( used to the format ) and keep outlook/voip/msn/misc on, or xreference material and the other is a Sony Bravia XBR 32" in 1920x1080 which is more or less main monitor.. and I also got my PS3 on it.
There is no need really for 2 32" , but no way would I want to trade my 32" for another 19" for symmetries sake =)
I have however, considered getting a 2nd 19" and sticking it on the other side of the 32", for yet more space.... and that symmetrical look.
But like most things, is a matter of preference.. however there is no technical reason that makes have 2 identical monitors superior.
