Like Airbnb, Linkedin and MySpace?? You can handle even large codebases well with Node. Callback hell is overrated since a large chunk of your code still stays synchronous for most server side rendered Node.js sites. At the end you implement user concurrency not in your app rather in some load balancing entity abstracting this away from you core app logic. Then, writing a Node app isn't much different than writing a Ruby or Python app (if using the right patterns/tools/libs).
And you get amazing speed: I think most didn't get how fast Node.js is -- it's factor 100 compared to any other traditional scripting language (i.e. Ruby). Once people learned this they won't go back.
Second, you're citing company's that use node in the niche roles that work great for node. For example LinkedIn uses node for mobile rendering, they use Java for everything else (http://hurvitz.org/blog/2008/06/linkedin-architecture) and (http://engineering.linkedin.com/technology). I really doubt that if anybody saw LinkedIn's use of node relative to their use of everything else they would call it "large".
Now relative to most Python and Ruby projects out there...
Yeah - you can use node for large projects