Obviously screen resolution plays a big part in this. At work (where I have a dual screen 1280x1024 setup) my browser windows will always be maximised. Whereas at home (where I run in 1920x1200), maximised browser windows look ridiculous.
I can't help but throw in a quick moan about current operating systems here. It may be a few years now since I stopped using RISC OS, but the window management system is one of the things I miss most from it. In Windows, giving a window focus makes it immediately jump to the front of the stack, which makes it difficult to use multiple windows at once without craftily resizing them so they don't overlap. In RISC OS, windows only jump to the front of the stack when you click on the title bar. You can type into/resize/move windows around regardless of whether they're partially obscured by something else. This makes it much easier to work with multiple windows at once, e.g. to type some code into a maximised text editor window whilst referring to a list in a smaller window you have open.