It's been a long time coming (for the nth time..), but we're scheduling a deployment of HTML5 across the Wikimedia cluster [1]. This is set for Monday 17th September at 18:00-20:00 UTC [2].
The intention is to set $wgHtml5 [3] to true everywhere. It's been running on MediaWiki.org and our 2 test wikis for quite a while, and other sites like translatewiki.net with no issues.
The intention is to leave it enabled unless it causes major problems. If you're running an application that screen scrapes, shame on you; you've had enough notice to get it fixed! ;)
Now is the time to fix up your scripts and programs (where necessary), tell your friends!
Sam
[1] https://bugzilla.wikimedia.org/show_bug.cgi?id=27478
[2] http://wikitech.wikimedia.org/view/Software_deployments#Week_of_Sept_17