I understand there has been at least some discussion (not sure how
much code there is) for Jaiku to make use of PubSubHubbub, and Jyri's
blog (http://www.zengestrom.com/blog/2010/02/the-buzz-is-out.html)
makes it clear that Jaiku was a major inspiration for Buzz.
There have been a couple of threads on Jaiku already about this, and
an initial code patch has been submitted for checking (see this thread
http://www.jaiku.com/channel/jaikuengine/presence/6b505df466c54c838f17215f7a0ff4f2
)