On a PC, the mouse cursor always gets in the way of what I type.
Think about it -- you use your mouse to click inside a text field, but unless the cursor is intentionally moved aside, it interferes with your ability to read what you type. And good luck if a tooltip happens to pop up under the cursor; that blocks pretty much everything. It's like trying to drive a car when all of a sudden someone splashes black paint all over the windshield. Not cool.
On my Mac, as soon as you type, the cursor disappears. Move the mouse again, and voila! It's back! What a simple, nice freaking touch!
However, every time I'm forced to use a PC, either for work or when I use bootcamp for miscellaneous causes, I'm confronted with this horrible oversight in basic design flaw in user experience.
Geez, Windows has been out for thirty some odd years now, and nobody at Microsoft realizes that pointing and clicking has nothing to do typing...