works really well.
Just tired it yesterday and am really happy with the result.
Basically (as far as i can see) you have full control over your xcode project and can even add more functions by extending Ejecta and mapping your own js functions to nativecode.
By now only tested a basic game, which works really well.
Havent tried integrating the iOs Gamecenter till now, only took me about 5 minutes to finally do it with ejecta.
Going to check out facebook integration and some more stuff and will let you know about my results.
At the moment im trying to get things to work in iCade