If you're currently publishing your blog to a custom domain, because you wanted to use a non-Blog*Spot address with some of the shiny Layouts template features, maybe you're tired of the occasional problems. Maybe you require the automatic redirect from BlogSpot to the custom domain, and the BlogSpot URL is redirecting to a bogus, unwanted warning.
Whatever your motivation, it's not hard to go back to publishing on Blog*Spot.
Just go to your Blogger dashboard, and click on the Settings link for the blog. Then, from the Publishing link under Settings, select "Switch to: • blogspot.com".