I always find little things that drive me nuts that I'd never have expected to drive me nuts. One was my slightly different keyboard layouts between home and work that I complained about long ago. Another is the positioning of the buttons on my Quick Launch bar on my taskbar at work.
On the machine at work where I do all of my mail and that sort of thing, I have three buttons between Start and the main taskbar buttons:
I reinstall Office at work a lot; every week or two, to pick up the latest versions. When Outlook is reinstalled, the Outlook icon moves to the very right. For some reason, that's very obviously wrong to me; I see that and immediately recognize that I don't like it. But, I never remember whether I like it in the first spot or the second spot. So, I pick one at random. Half the time I pick incorrectly. For the first few minutes it doesn't bother me. But, then I get to a point where I stop looking at the icons and just click the second button to start Firefox. If I put Outlook there instead, I end up launching Outlook, and get angry. Somehow I couldn't remember which order to put my icons in when I was trying to remember, but as soon as I start trying to start that application, I instinctively know which button it's supposed to be.
One of the themes for Mac OS X had the window command buttons (close, windowshade, and maximize, I think...) all look the same, as plain grey bubbles. I always thought that was a curious design decision and I still think it is, but it's definitely sound in that I'm not actually looking at icons that I use a lot; I just remember their positions.
As a very related side note, I never actually use the PowerShell icon. I just end up starting a regular command prompt by pressing Win+R, typing "cmd," and pressing Enter. I've done it this way forever. It will take an eternity to get over that... I still close maximized windows by double-clicking the left corner, Windows 3.1-style. That ingrained behavior is the sole reason that I use a regular command prompt instead of a PowerShell prompt. I tried putting it in my Quick Launch so I'd use it more, but I don't.