• You can build mobile apps with PhoneGap Build. jQuery Mobile makes it really easy. You can deploy to the market place in Apple’s app store, and Android’s, and others so quickly your head will spin.
• Build large scale client side web applications. Frameworks like Backbone JS, Knockout JS make this much simpler.
• Access large scale data installations. JavaScript is now a first class citizen with regards to data access – whether you’re hitting MongoDB, CouchDB, or RavenDB. Or, even WCF-RIA or OData to access .NET based data sources.
• Develop screaming fast scalable web back end services using NodeJS.
• Securely and effectively process payments with Stripe or even TSYS MultiPASS.
• Develop Native Windows 8 apps with Chakra.

I’m not sure this can be overstated: never in my career has one skill set been applicable in some many areas all at once.