Recently I worked on a website with a lot of forms, and decided to use HTML5 form validation to make my life easier, with a JS fallback for older browsers. It turns out that Webkit added support for HTML5 form validation, then found a problem, so they switched off the implementation without switching off the exposed API. So every JS fallback that tests for the presence of the HTML5 methods on form elements will assume that HTML5 form validation is implemented, and leave the validation up to the browser... which doesn't actually do it at all.

That means server-side validation, which of course one needs to do anyway. But it's not to hard to imagine somebody making a site during the brief window when Chrome supported HTML5 form validation, and then discovering their site broken in Chrome a few months later.

H.264 is scheduled to be broken in Chrome in exactly 6 weeks (given Chrome 9 came out this week)

Please see my other post: http://news.ycombinator.com/item?id=2189846