[reptation]

Not a semi-colon but -

Setting up a GPO to push Microsoft updates to clients in an AD domain, I spent ~8 hours debugging why the clients couldn't connect to the WSUS server. It turned out that there was trailing whitespace in the server URL text field that was getting parsed.

As a side note, this type of story IMO doesn't actually play that well in interview situations.

[rurounijones]

Everytime I receive input from a human source I remove leading and trailing whitespace. (I have never had a situation where it was needed)

Far too many instances of copy/pastes including those bloody things.

[b3lvedere]

Every time i need to copy/paste some important text into something, i run it through notepad so it kills all the (meta)code that may be hidden deep inside the text. I know it may not kill the whitespaces, but it's usually the first thing i do when i get copy/paste crap like that.