Mark told us HTML5 is not good enough (not ready) for building complicated native application. I don’t think people all agrees with Mark and obviously Sencha is one of them.
Some engineers from Sencha have released a website (a WebApp) created with HTML5 technology based on Sencha’s HTML5 framework. It’s called Fastbook. They published a demo video compares the performance between the native Facebook mobile client and the WebApp runs in the phone’s browser. I heard about this from infoQ so you maybe you can goto there for more details.
I tried Fastbook just now and it didn’t work on my Android 4.1 system very well. After I gave the permission to Fastbook for accessing lots of stuff in my Facebook account, it kept showing loading spinner for a long time. I had to click Back to quit browser after several minutes. When I tried to open the website again, it showed a blank screen and nothing more.
Although the site didn’t work me, I don’t think HTML5 is THAT terrible for regular native client development. But we do see some disadvantages such as lacking of handy IDEs, but I do think this would be resolved in the recent future. We are trying something new with HTML5 in our products and let’s see how it goes.