I've seen this and it looks very interesting, but there are two problems - there's such little documentation I can't see any obvious way to actually use it, and it seems to require you set up a full blown XCode development system on a Mac. The reason I like PhoneGap so much is the build system is so simple. Without PhoneGap build, to make an iOS app you need to own a Mac, download XCode, download a bunch of SDKs, install everything and run the compiler. The whole system is designed for programmers. Same story for Android: you need to download hundreds of megabytes of the Eclipse IDE, Android SDK, configure the compiler correctly, and on and on. I did it myself and it was a massive headache, and I'm a programmer! And again for Symbian, and again for all the others. Compare that to PhoneGap Build: upload, wait a moment, done. If we tell people to get these development systems we're also obliged to help them get it working, which is really complicated, slow and difficult. So I see PhoneGap as being much more suitable for the non-technical easyness of Construct 2. AppMobi don't appear to have a similar online build service.
So PhoneGap is OK but not great - iOS 5 performance is OK for simple games and Android 4 (Ice Cream Sandwich) should be similar, but it's still not quite there. I'm hoping for WebGL to be supported on phones soon. Our runtime already supports it and that should enable close-to-native performance in HTML5.