Google Code project page for PuSH.
#pubsubhubbub
Implementing PubSubHubbub subscriber support: A step-by-step guide
Implementing PubSubHubbub subscriber support: A step-by-step guide
A nice step-by step (with some gotchas) tutorial on PuSH-enabling a feed client.
Superfeedr
“Real-time feed parsing in the cloud for web-developers”