I kind of dislike progressive loading; certainly the type that's used as an (hypothetical) example in the article. The squashed blurry bad-quality image isn't all that useful, and you're never actually sure if it is or isn't loading a better version in the background. I'm not so sure if it's really better UX, because either 1) you care about the image quality in your use case and a blurry version just won't do, or 2) the image quality isn't all that important and you should be serving smallish images anyway (like the Guardian), possibly clickable to load a high-res version for those who desire it.