Yeah, it's fast, but speed and concurrency aren't everything
No, speed and concurrency aren't everything, but they are damn important. I've heard many saying "I'll stick with PHP / .NET / Ruby / etc. for now, and if my website will get thousands of visitors per day, I'll simply scale-up my servers".
Well, apparently that's easier said than done. Even GitHub has occasional issues - I'm sure many have seen the annoying unicorn error page from time to time :-).
And nobody can guarantee you'll be rich before you get thousands of visitors on your website. Usually it happens the other way around, if at all :-).
Plus, I've heard cases of websites that were simply put down by Google's crawlers. And you certainly don't want that happening to you, because in the online business today, if Google is not "your friend", you simply don't exist :-).
So, being able to handle lots of traffic while your website still feels "snappy" will never be wrong. Especially if you don't have to pay a lot on infrastructure or sacrifice maintainability (nobody would write in plain C to achieve that).
There aren't enough good Node.js developers out there
Also, the same applies to every other platform, framework or language. There are many developers, but few of them are good. Still, most of the times, a healthy dose of common-sense will make up for the lack of perfection.
Big corporations aren't using it yet
Fine. Big corporations are using .NET and J2EE, at least in my part of the world. Well, if that's where you wanna be, stick to .NET and J2EE, make sure to go regularly to Microsoft and Oracle seminars, and maybe have a look at Scala :-).