I am keeping an eye on the pubsubhubbub technology since its first day, it is a very simple, yet interesting technology to make RSS/Atom feeds really fast without polling. I wrote my own component called 'SubHub', it is running for a couple of weeks now, it is receiving tons of Atom and RSS messages from popular news-sources like nasa, cnn, bbc and the few thousand other, through pubsubhubbub. Thanks to this hard-to-spell technology, I do not poll at all :-)
The developers envisioned a distributed network of hubs and streams and sure it is distributed by design. What I wanted to know is how distributed is it, since my first guess was that Google will have a little dominance in it. For example blogger.com rss feeds (including Dummy Warhead's) are pointing to google's pubsubhubbub server. The WordPress guys were also very active and they implemented their WordPress plugin, which is turned on in all the wordpress.com blogs, but they only use it for their own content while Google's service is used by anyone... and almost everyone.
Enough talking. Let's see, who is doing most of the work in pubsubhubbub:
The graph was generated from the web server log using the usual linux commands.
So the two upcoming players are SuperFeedr and Pheedo, looks like they are special services for special customers. There might be some minor players in the technology, but I haven't found them yet.