One of the most annoying things about computers these days is the number of applications that put everything in tabs, and/or modal dialogs. The whole point of a GUI, to me, is that you can view information from multiple places side by side, not just swap between them. In the mid-80s, Apple wrote copious documentation about why modes, and modal dialogs, are bad, and tabs were not a standard part of the interface either.

As far as multiple screens go, it's not just viewing things side by side, but having boundaries to snap to. Maybe it would be handy to kind of divide very large monitors into subscreens...