This article says no, plain text is a lie. I don’t see it that way. The article is really talking about making sure you have your encoding correct and it does a great job of explaining why. To me, however, plain text in English is ASCII. It’s been around for over 50 years. It will render correctly in all cases. I recognize that the Internet has made it necessary to provide for other languages and that is where Unicode comes in. For that, you definitely have to make sure you announce your encoding, as the article says. The article also recommends that you read Spolsky’s article about encoding. I second that recommendation.