Things really took off a few weeks ago at Google's IO conference. GOOG officially put its chips in the HTML 5 pot. This should not have been a surprise, as Google has invested in improving browser technology first through Gears and then through its own browser, Chrome. Of course Chrome actually uses the now ubiquitous WebKit for its rendering engine. This is at the heart of not only Apple's Safari browser, but also the mobile browsers on the iPhone, Android, and Palm Pre. Google used the "standardization" of WebKit on mobile devices to deliver mobile versions of GMail and Calendar thus punting on native applications.
So HTML5 is the future, right? Not so fast. I know it seems this way to a lot of people, especially the emphatic fans of open standards. However, those guys live in a different world than I. In the world I live in, browser fragmentation is at an all-time high. In a world of fragmentation, standards are an amusing concept. If history has taught us anything, it is that standards are set by whoever has the most users.
This has long been a source of pain for Google and others. In all fairness, IE8 implements some of the HTML 5 features, but not all of them. Also, the IE family of browsers has been losing share for several years. However, it is going to be awhile before web developers can forget about IE6, not to mention IE7. Given the update cycle of IE in the past, we can expect the older versions to stick around a long time before IE8 finally becomes the king. Again it does not even implement all of the highly touted HTML 5 features. Maybe more will be supported in IE9? How long before that becomes the dominant browser?
My point is that if you want to hitch yourself to HTML 5, you are not hitching yourself to Firefox, Safari, and Chrome. Well ok, you can hitch yourself to those browsers (or IE+Gears), but you are saying go away to 60-70% of the world. So assuming you don't want to do that, then hitching your app to HTML5 means hitching your app to future IE adoption. That just seems like a scary proposition to me.
But what about mobile devices? Here things are clearly better. Again the standards are set by the dominant player. WebKit is the dominant technology in high-end mobile browsers. Still there is fragmentation. The exact same APIs do not work on Mobile Safari as on the Android browser (don't know about the Pre.) Thus you may have to do some abstractions to smooth over the differences. Oh wait, that is starting to sound a lot like the situation with desktop browsers... Anyways, many HTML 5 features are present on the iPhone and Android browsers, so you have much more latitude to use them. However, there is another, more important question to answer when considering going down the path of GMail/Calendar on the iPhone/Android. Can a browser based be as good as a native app? Probably not, but maybe it's "good enough." However, I have to wonder, how many GMail users use the GMail web app on their iPhone instead of using the native Mail application? The GMail web app gives you all of the features you are used to, like conversations, labels, stars, and awesome search. The native Mail app provides none (or at best much weaker implementations) of this, but yet I would guess that most people still prefer it over the web app.