Generally I wasn't really that impressed by the demo. Sure, the integration is nice, but I don't see how that's different from most other IDEs. But what struck me as a bit odd was the presenter stating a preference for vim, and then starting to edit Objective-C like all you've got is your cursor keys plus tab.
So, yes, another IDE, yay. And if you work at FB, sure, mindshare alone is probably worth it. But why would one give up normal mode/macros/elisp/abbrevs etc. for that?
Now don't get me wrong, I totally understand different preferences, and if your current editor is e.g. TextMate/Sublime or an IDE like PhpStorm/Eclipse/Xcode, I can see it. But if you start with the premise that vim is the One True Editor, why would this be the switch reason, whereas IDEs before didn't get you there?
No problem with another flower in the garden of editing, I just thought the sales pitch was a bit weird.