WebSockets in PHP/CI/jQuery

Hei guys. I am very interested in this topic. I have tried node.js in heroku and it seems pretty nice. A couple of doubts:
1) In terms of performance websockets are more resource intensive for the server then normal http request / responses ?
2) In terms of the application itself, do you think it's easier or harder to build with websockets? Or maybe it doesn't even make sense to use websockets I dunno... For example, blog, institutional website, ecommerce, and so on...
3) What are the best scenarios to use websockets? I am not sure if websockets are here to completly dominate or if they are resource intensive and should be used for real time applications or widgets... for example... maybe use a webchat that will be in an iframe inside your normal website?

I would love to be more enlighted on this... I have made a simple chat application on heroku with a couple of lines. It is super effective in terms of code and performance for the user... I don't know about the server though...