But the question still remains, why should a designer waste her time in learning HTML5, when HTML5 specification is not yet complete. It makes no sense to invest time into something, because your nerd friend wants you to learn
HTML5 adoption is happening at a faster pace then you can imagine. All major browser vendors are now supporting HTML5, some have already started shipping HTML5 features in the current browser builds, while others are busy catching up. Not only browsers but several websites like youtube, facebook, scribd etc. have started HTML5 based versions. So unlike previous improvements in HTML, such as CSS, which took years to be adopted by browsers, HTML5 adoption is progressing at a healthy pace.
HTML5 is a standard that has took many years into making, with input from various software vendors and individuals, including designers. This process has ensured that most commonly used features of web development are supported by browsers natively, without need of any external libraries. At the same time, HTML5 has tried to add tags that will make content layout easier along with support for microformats. This makes presentation as well as sharing of data easy.
Though you may argue that HTML5 specification is not yet ready, then how are browsers implementing HTML5 ? This is acceptable. HTML5 is a big standard. It is so big that during the discussion stages, HTML5 specification has to be broken down into couple of smaller standards. Standardization process require drafts to be published and comments be received. Once drafts are published, the core ideas /features/processes/algorithms are rarely changed. Although it will take couple of years for the full specification to be ready, test suite be prepared and browsers passing those test. You can safely assume that the features/algorithms defined in the standard will not change.
So, no harm in investing time into learning HTML5 as it is going to become the defacto standard for web based applications in the decade to come.
How to learn HTML5 ? There are lots of tutorials available on the internet on HTML5. You can also, keep an eye on this blog, as there will many posts in near future, explaining various features of HTML5.