Implementers of the PubSubHubbub specification can create their own hosted hub solutions, but for those who would like to work off what is currently available in the market, there are a number of hubs and implementation services to choose from.
Anyone can create a PubSubHubbub server, and if an open hub is available, anyone can use it. Here are several of the implementation services and hosted hubs currently available:
Google App Engine reference hub: http://pubsubhubbub.appspot.com/
Superfeedr hosted hub: http://superfeedr.com/hubbub
SubHub Django integrated hub: https://code.launchpad.net/subhub
Ayup hosted hub: http://ayup.us/
WordPress plug-in: http://wordpress.org/extend/plugins/pushpress/
RabbitHub erlang implementation: https://github.com/tonyg/rabbithub/#readme
Wolverine Twisted Python implementation: https://github.com/progrium/wolverine#readme
WebGlue Ruby implementation: https://github.com/zh/webglue#readme
Subfeedr Perl implementation: https://github.com/miyagawa/Subfeedr#readme
These are excellent starting points for both leveraging hosted open hub solutions and utilizing current implementation examples of the project.