[nehz]

Yes.. having a large amount of concurrent users (>100,000) is definitely a challenge, and polling each time adds to the load as you are creating a new connection every time.

Our approach was based on horizontal scaling of commodity hardware (on Amazon EC2). We have X number of worker instances serving clients and they internally publish and subscribe using a Redis cluster. Have a look into Redis, ZeroMQ or RabbitMQ.

But definitely give our service a try in your free time or for your side projects :)