In fact, I'd like to be able "attach" a terminal to another app for switching purposes. It's probably the same with finder and browser, (I'd add text editor).
A "one task, one app" type of app should have it's functionally-related windows grouped for switching, but a highly multipurpose app where different windows do not serve different functions should be separate.
This is what I use Multiple Desktops for on Ubuntu - I group applications by task, so that each task has one desktop. Then I just switch between desktops, and very rarely between individual applications (as they don't normally overlap).
Trying to work on Windows without good multiple desktop support is horrid now.
A "one task, one app" type of app should have it's functionally-related windows grouped for switching, but a highly multipurpose app where different windows do not serve different functions should be separate.