I think that Facebook has enough resources that they should go native. But I also don't think that HTML5 is as bad as Facebook has made it look (having made an HTML5-native hybrid app myself), and I think it's still a valid choice for smaller outfits.
That said, my greater concern isn't performance on HTML5, it's interface. iOS, Android and (particularly) Windows Phone have very defined UI metaphors and design styles that vary a lot- if you have to replicate all of them then it removes a great deal of the benefit of a cross-platform app.
The answer may be, weirdly, in C#, using MonoTouch and MonoDroid. You'll always have to tailor UI to each OS, but having an entirely consistent backend to that UI is an attractive option. I just haven't managed to convince myself to drop the cash on a license yet, though.
That said, my greater concern isn't performance on HTML5, it's interface. iOS, Android and (particularly) Windows Phone have very defined UI metaphors and design styles that vary a lot- if you have to replicate all of them then it removes a great deal of the benefit of a cross-platform app.
The answer may be, weirdly, in C#, using MonoTouch and MonoDroid. You'll always have to tailor UI to each OS, but having an entirely consistent backend to that UI is an attractive option. I just haven't managed to convince myself to drop the cash on a license yet, though.