On the Codex on Post Thumbnails, I see:
Post Thumbnails is a theme feature introduced with Version 2.9. It was quickly changed to Featured Images with Version 3.0. Post Thumbnail, now Featured Image, is an image that is chosen as the representative image for Posts, Pages or Custom Post Types.
On the changelog for Version 3.0:
Change Media UI labels from "Post Thumbnails" to "Featured Image"
Is there any difference in behaviour of post thumbnails and featured images, or was in 3.0 only the name changed? Why did the name change? It is a source of misunderstanding, as the image size is still called
thumb, while it on the UI everywhere says Featured Image.