On a day-to-day basis, this is what I hate MOST about Vista: how it arrogantly wastes screen space.
Screen space is one of the most precious resources on any computer. Even if you’re running a 2560×1600 monster, those little pixels cost money, and there are never enough of them. When your screen starts to fill up with junk, you want to know that it’s useful junk, not just some idiotic crap that serves no purpose.
Vista uses screen space more wastefully than any previous OS. Just to display a file listing, it throws away about an inch and a half at the top of every Explorer window, to display controls I never use. Gone is the useful, simple, compact menu bar, which displays a maximum number of options in a minimum of space. Now you’ve got a big border (without even the former justification of showing the window title!), a Search field (even when you’re not searching for anything), a button bar (that works like a menu but takes up more room), and, most idiotic of all, column headings (even when you’re in a List view that doesn’t have any columns!!!). The “optional” menu bar, which you will need, is on top of all that.
Could this be any dumber??
Why, yes. Yes it could. Remember, this is Vista.

Check the bottom of the window. The nice, neat little status bar, that offered so much useful info in a single line, is now replaced by a gargantuan status “Panel,” complete with neat little headings, info you never use (“Shared with: Everyone”), and a little thumbnail (that repeats the one already shown in huge size in the main window!!). And believe it or not, that’s the best case! Check the next screen cap: about a hectare of baby-blue shaded vacancy, plus a huge, utterly meaningless icon, to tell me there are “35 items” in the window!! Arrrrggghhh!!!!

But it goes on. You can also display a tree panel at the left, and a preview pane at the right. By this point, I can only assume you’re looking at one file icon in a little keyhole in the middle of your monitor.
Does it look nice? Oh, sure. Gorgeous. But could it have all been designed to work efficiently, and still look good? Hell, yeah! By anyone who actually gave a cr@p about usability. Clearly, that no longer includes the new marketing-driven Microsoft. Vista is like an aging whore: thick layers of makeup smeared on top of a commodity that is way past its “best by” date.
If I could moderate Vista’s cavalier usage of my monitor, I could almost live with it. Though I’d still hate it for about 1,000 other reasons. Not to mention on principle.