Fossil

I'd liken it to the "preview comment" button here - that one roadbump causes me to put far more care into what I'm emitting than if there'd just been a single post button (even if it doesn't seem like it sometimes). I've used many other UIs for committing what I type to the internet, and it feels like there's a definite correlation between the overall quality of results in some of them and whether they let (or require) you experiment and make mistakes in private.