It's amusing how the switch to widescreen monitors have made vert the limited resource now, rather than horiz. All our UI layout practices were invented on 4:3.
Since I'm using a 16:10 monitor it works out nicely. Opera also has a problem of not clicking the tab if you put your mouse all the way at the top of the screen when the tabs are at the top of your browser. However if your tabs are on the side you can throw your mouse to one side and be guaranteed to click a tab.
If you bring up a window, and it's too small, you could either: A. Drag it to where you want it, and then fiddle around resizing it so that it's big enough and doesn't overlap anything else important, or B. Maximize it in one click, do what you need, minimize it again.
Additionally, Windows windows have lots of chrome when unmaximized, and this tends to discourage heaps-of-small-windows layouts.
Try out Winsplit Revolution. The help page gives a nice overview of the functionality: http://www.winsplit-revolution.com/help
It's free and works great for positioning windows. You can position windows using hotkeys and create custom positions/window sizes. WIN+ALT+Numpad 7 will place and resize a window in the top left of the screen, WIN+ALT+Numpad 6 will place a window on the right side of the screen and take exactly half the width, etc. It's become second nature to me and I rarely have to worry about manually placing a window.
How on earth you work with Twitter always visible onscreen I don't know. Do you get anything done!?
I was referring to the very few 16:10 monitors available now, almost all of them are 16:9.