Speaking of mistakes in usage, here's a funny anecdote:
Yesterday I had to talk with our Main Street Association president about some invitations I'm designing for her. She was rather flustered about a list of things she had to get done, most of which involved asking various people for donations. She said to her assistant and I: "All I do is ask for money. That's my job, is begging people for money! I am a professional lech!"
I'm pretty sure she meant leech, bless her heart. I stifled my shocked giggle pretty well.