Here's something that rankles me whenever I'm knocking out words on the computer. It's that little wiggly red line that appears as you type, you know the one, it shows up underneath words that are, ahem, miss-spelled. Like colour for example, or organised, or the double whammy - colourisation.
Now i am fully aware of the fact that this is so-called US English and I could just change the dictionary settings to International English, but you got to admit it's annoying having to change all the defaults to get things to work right (don't get me started on US letter paper size).