Niki Tonski with a very well-illustrated post on centering text, icons, and UI elements.

The problem is explored in great detail. Every big company fails at this. Type (font) design and UI design and icon design are all part of the problem.

After the build-up, this part killed me:

What can be done: icons fonts

STOP.

USING.

FONTS.

FOR.

ICONS.

I recommend looking at the pictures to spot all the annoying alignment problems and have a good time with this.