Hey, just saw this thread today, thought I'd read through the replies and post one of my own. If you were to ask me about implementations of features in various OSes I'd have quite a bit to say.
Let's start with menu bars. Both Windows' and Mac OS X's implementation of menu bars have their upsides and downsides. The "global menu" approach used by Mac OS X obeys Fitt's Law the best - you always know where to find the menu bar, no matter where the window is located. However, when multiple monitors are involved, this approach's limitations stand out like a sore thumb. Windows attaches the menu bar just below the title bar of each window. This doesn't fall apart on multiple monitors the way Mac OS X does, but it has s significant downside: It's not always in the same spot, due to differing title bar sizes and window positions, and thus disobeys Fitt's Law. There is a solution to this conundrum, though... and the successor to Lion could conceivably implement such a thing with the changes made to Lion. That is: Add an option to move the menu bar wherever the active application goes. Since even Java applications can have their state saved (though the support is rather primitive), and Mac OS X already has the ability to fix window sizes if they become invalid for some reason (which will happen more often if this suggestion is implemented), the days of needing to mouse over to another screen just to figure out where your menus went will be over.
The second feature from Windows I'd like to see a (better) implementation of on Mac OS X is the ability to further customize the sort order of Finder windows. There are plenty of times when I'm interested only in a sub-folder of a particular folder containing thousands of other files (that aren't folders). Yes, sorting by kind partially addresses this problem - why can't we put the kinds we want to see first in the sort list? Maybe this is already doable in System Preferences -> Spotlight, and I just haven't tried.
Finally, we need a sensible, one-button "Make All My Windows The Same" feature, in View Options. The current system is a mess - there's no way to tell what the defaults are while a non-default window is open, for one thing.