Mac OS X / Windows Philosophical Differences
It's true, the Maximize button is one of those philosophical differences between the Mac OS and Windows. The other recently discussed one is font smoothing, and there are still a couple more waiting to be discovered / discussed: Close vs Quit, Switch Windows vs Switch Apps, and Replace vs Merge.
Maximize vs Size to Content
First, on Maximize. Generally I agree with Jeff that the Maximize button should maximize a window. I understand the Mac philosophy that maximizing is often a waste of real estate - and it may be that because Apple generally has the biggest displays, it more often makes less sense to maximize on the Mac - but the option should be there when I want it. Maybe via Cmd-Click on the green button, or something like that. Plus, unlike browser windows, some apps make good use of whatever real estate you give them - by giving you a larger view of the document you're working on, for example.
Close vs Quit
Close vs Quit is one where I disagree with Apple's choice. The issue is that on Windows, when you close an application's last open window, the application quits. On the Mac, the application stays in memory. You can see this on the Mac when you launch, say, TextEdit, and then close the window that opens. TextEdit is still shown on the menu bar, and the dock shows a triangle underneath the application icon. The triangle is how the Mac tells you the app is still running.
I find that both myself and my wife occasionally need to go and "clean up" all the extra applications that are still running, because we've closed the window instead of quitting the app. I'm sure it's something you get used to, but apps launch quickly enough that I don't see the value in keeping them around.
Switch Windows vs Switch Apps
This difference is how Alt-Tab or Cmd-Tab works. On Windows, this switches you through all top-level windows (though not all windows, frustratingly enough). On the Mac, it switches you through applications.
If you have two Notepad windows open on Windows, they'll both show up in the Alt-Tab list. If you have two TextEdit windows open on the Mac, all you see in the Cmd-Tab list is TextEdit. You have to use Cmd-` (the back-tick key) to switch between the windows of a the application you're currently working with.
In this case, I don't really see that one is better than the other; they're simply different.
Replace vs Merge
This one is a bit dangerous for a Windows users. Consider this scenario: You have a folder on your desktop called June Photos, and you also have a folder with the same name on a memory stick. You grab the June Photos folder on the memory stick and drag it to the desktop.
What happens?
On Windows, the contents of the two folders are merged into the folder on your desktop. All the files in both folders will exist, and any that were in both places will be replaced after prompting you.
On the Mac, the contents of the folder already on your desktop are deleted, and the folder from the memory stick is copied onto your desktop. You will lose any photos already in the June Photos on your desktop. (There is appropriate prompting, but if you're used to the Windows behaviour, you may just ignore it since hey you know how it works already).
I definitely prefer the Windows behaviour here. A big factor here is that often the reason you're merging two folders is because you were moving data from one place to another, and for some reason the move didn't complete. You want to resume the move but if you use the same gesture you used to start the move the first time, the stuff that's already been moved will be deleted and you'll end up with just the remaining files.
These topics are being discussed now because so many people are dabbling in Mac OS for the first time, and of course different is often initially perceived as "wrong". Better to go into it aware of the differences so at least you can give them a fair evaluation.