Is it just me,
or is everything that people are enthusing over about html5 already available in, say, flash?
Mature toolchain, massive user and developer base, blah blah blah. I guess we should probably be thankful Adobe haven't tried to give us FlashOS yet.
Me, I see two problems in the bright HTML5 future. Maybe three. Firstly, what is stopping a dominant vendor doing the old embrace and extend trick? Google and Apple spring to mind. Have a think about what Chrome's NaCL is intended for. Secondly, javascript/html is a bloody awful dev platform. I've worked with various languages and GUI frameworks in the past, and whilst few have actually been very good they've all been significantly nicer to program in than javascript, and mildly more convenient for presentation layout than HTML/CSS. Having to code in JS for the rest of my life seems a bit like a punishment.
Lastly, the whole 'write once, struggle everywhere' approach is probably quite familiar to most web devs. The problem has manifestly failed to go away over the last ten years. It isn't going to stop now. Platform providers are manifestly shit when it comes to supporting complex standards; why is this going to change? This problem is perhaps a subset of the 'embrace, extend' issue above.
When Silverlight, of all the unloved and unwanted dev environments starts to look good in comparison to the glorious new future, the world is very clearly heading in a bloody stupid direction.