Sven-S. Porst on the Mac OS X 10.5 “transparent” menubar:
The first is that the menu bar is an essential part of the Mac GUI. And making it harder to discover und use just seems counterproductive. Having a less than white menu bar, will necessarily affect the contrast of the menu items’ black names to their background. And as desktop backgrounds are essentially unpredictable — all screenshots here come from my standard set of randomly rotating desktop backgrounds — there is just no way Apple’s engineers could come up with one algorithm to rule them all.
This is easily one of the most questionable UI changes I’ve seen Apple make with the Aqua interface and there is seemingly no serious benefit I can think of that isn’t offset by the negative HCI experience. Thankfully the menubar can be fixed with some basic command-line hacking.