I have a love/hate relationship with the darn things. While I try to avoid them, I had to use one just a couple days ago. So, to answer your question, a couple of days ago. But I know lot's of people who love them and when present I see them being used by others with high frequency.

Other than it being loosely related to the technology of money and shopping, what does your question have to do with, "A Revolution in Money"? Specifically, what does the recency of an individual's interaction with a self-checkout machine have to do with the article?