I frequently have apps that need to be maximized across both displays. I agree that many apps do not benefit from that much space, but some apps will always need as much room as you can throw at them.
Actually, you failed to note the REAL problem about large displays. You can’t hang them off a good swivel mount arm, they weigh to dang much. Personally, I won’t live life without my arms, and until they make better arms or lighter displays, that alone will limit me around the 20" market.
If you haven’t tried them yet, I highly recommend it. YOu want convenience? It isn’t dragging a window around your displays - IT IS DRAGGING YOUR DISPLAYS AROUND YOUR DESK! Trust me - try it and you’ll NEVER EVER go back.
Just make sure you get the GOOD arms, not the ones that are just lamp mounts with stronger springs. Try something like this : http://www.memoryexpress.com/index.php?PageTag=page=filememx_menu=EmbedProductDetail.phpDisplayProductID=7948SID=