The new Safari Validator release is out, bringing HTML5 validation!
The service to validate the HTML5 pages is validator.nu. This means that, unlike W3C validation, the contents of the HTML5 pages are transferred to the remote validation.nu server, and processed there. Be careful that you don't submit pages containing sensitive information for validation! It's best to turn off HTML5 validation in the preferences when you're not developing an HTML5 website to be sure.
I've also added, upon request, a toolbar button. This quickly toggles the Safari Validator bar so you can reclaim the precious screen real estate when you're not interested in the validation results.
As you will probably notice (the most of you being designers and all) that the button image is just about the ugliest ever created, I can only agree. I'd have put the circle with the v-checkmark in there in grayscale, but Apple forces to use a (alpha) bitmap, and I didn't have the time to create a nice looking icon. If you're interested in making a decent logo for the toolbar button, let me know. Just make sure to only use black (and transparency).
Three other fixes are also included : the W3C validation results page is now shown again, and the border added by the extension at the bottom of each website is gone. Also, the embed shouldn't be injected into iframes anymore, so it won't end up in CMS rich text editors.