Does the PubNub Socket.IO SDK implement the presence feature?

Yes, the Socket.IO SDK uses PubNub presence today. To receive presence events, the Presence add-on has to be enabled. PubNub + Socket.IO is a feature-complete matching of the original Socket.IO framework released by Guillermo Rauch.

The PubNub version of Socket.IO is a complete rewrite to match features available in the original Socket.IO implementation.The PubNub implementation is faster and more capable and efficient. It allows you to scale automatically without need for investing in special Node.JS server infrastructure.