This morning I took the 70-480 Programming in HTML5 with JavaScript and CSS3 exam and passed with a 900. I figured since there was a free voucher for the exam I might as well try.
Go to http://www.microsoft.com/learning/en/us/offers/html5.aspx and get the voucher before March 2013 and before they run out.
This counts for the first test of the MCSD: Web Applications and MCSD: Windows Store Apps
http://www.microsoft.com/learning/en/us/visual-studio-certification.aspx
There is also free training for this at https://www.microsoftvirtualacademy.com/tracks/developing-html5-apps-jump-start which also has a companion Windows 8 App to follow along with the code at http://codeshow.codeplex.com/.
I also came across a free eBook: http://blogs.msdn.com/b/microsoft_press/archive/2012/10/29/free-ebook-programming-windows-8-apps-with-html-css-and-javascript.aspx.
We are trying to get all the developers at our office to take the exam before the free vouchers disappear. We have been doing study luncheons every week to cover the videos and talk about the skills measured (http://www.microsoft.com/learning/en/us/Exam.aspx?ID=70-480).