HTML5 Please
‘Look up HTML5, CSS3, etc features, know if they are ready for use, and if so find out how you should use them – with polyfills, fallbacks or as they are.’
HTML5 Rocks: Improving the Performance of your HTML5 App
1stwebdesigner: 20 snippets you should be using from HTML5 Boilerplate
Sounds stupid and listy but it's actually a good introduction to some of the more useful and practical pieces of the huge insane HTML5 Boilerplate (html5boilerplate.com).
Safari Developer Library
Powered by the WebKit engine, Safari offers leading performance, compatibility, and a great set of built-in web development tools.
When Can I Use
"Compatibility tables for features in HTML5, CSS3, SVG and other upcoming web technologies."
Dark Crimson Blog: Getting Started with HTML5 Local Databases
Saved for later…
Adactio: Journal: Parroting Pareto
Discussion, in regards to mircoformats and WHATWG , of the value of the "Pareto Principle," which states that 80% of the problems should be solved with 20% of the effort.