Speaking as someone writing a fairly major HTML5 iOS app using Jo and PhoneGap: this looks like a very helpful way to take the make-work out of the case where you have an app that uses no native functionality, and is not in any way optimized for best appearance.<p>That's not a knock - a lot of people have that use case, and spend a lot of time on their own systems for deploying to multiple platforms. Consider internal apps, for example, that don't have to be massively visually slick and polished.<p>But ... given the very large differences between even similar platforms, and even between versions of platforms, you're not going to be getting much from this if you are building ultra-slick apps in which you really do need consider, say, how hardware acceleration or browser quirks fit into the picture.