The automatic plurals don't count the word just once, so it's annoying if you get a plural by accident that you didn't want. Before I realised that hitting Enter rather than the guess button gave plurals, I had a WTF moment when, entering i in a mathsy-looking piece, 'we' appeared as well.

In addition to looking for clues (including thinking hard about oddities) and counting letters, the other thing is to not hurry to put in non title words if you're pretty sure of them, unless you need them to help you make sense of more of the text. I shouldn't have bothered putting in the overall subject area today.