23. Pixel font sizes
“Your text is too small for me to read, and you’ve sized it using pixels. I can’t resize it using Internet Explorer, the only browser I’m allowed to use at work.”
Prior to version 7, Internet Explorer was afflicted with a bug: it wouldn’t let visitors resize text specified in pixels. Unfortunately, a lot of people are still stuck using this outdated browser. The solution? Use any other unit of measurement to define your font sizes. We’re quite fond of ems.