I'm currently creating a website using PHP and the Kohana framework.  I want to site to be able to use real time (or near real time) data (e.g. for chat and real time feeds).  I need it to be able to scale to thousands of concurrent users.  I've done a lot of reading and still have no idea what the best method is for this.
Does anyone have any experience with StreamHub?  Is it possible to use this with PHP?
Am I digging myself into a hole here and need to switch languages?  I've looked at node js and nowjs, but I'm weary about coding a while site in Express (I wonder about security holes, code maintainability, lack of a good ORM).  I've read about Twisted Python, but have no idea what web framework would work well on top of that, and I'd prefer not to use Nevow - maybe Django can be used well with Twisted Python?  I'm just looking to be pointed in the right direction, so I don't go too far in PHP and realize I can't get the near real-time results that I need.
Thanks for the help.
I've looked at node js and nowjs, but
  I'm weary about coding a while site in
  Express (I wonder about security
  holes, code maintainability, lack of a
  good ORM).

I can personally vouch for code maintainability if you can do JavaScript. I personally find JavaScript more maintainable then PHP but that's probably due to lack of PHP experience.
ORM is not an issue as node.js favours document based databases. Document based databases and JSON go hand in hand, I find couch db and it's map/reduce system easy to use and it feels natural with json.
In terms of security holes, yes a node.js server is young and there may be holes. These are un avoidable. There are currently no known exploits and I would say it's not much more vulnerable 
then IIS/apache/nginx until someone points a big flaw.

I want to site to be able to use real
  time (or near real time) data (e.g.
  for chat and real time feeds). I need
  it to be able to scale to thousands of
  concurrent users.

Scalability like that requires non-blocking IO. This requires a non-blocking IO server likes nginx or node.js (Yes blocking IO could work but you need so much more hardware).
Personally I would advice using node.js over PHP as it's easier to write non blocking IO in node. You can do it in PHP but you have to make all the right design and architecture decisions. I doubt there are any truly async non-blocking PHP frameworks.
Python's twisted / Ruby's EventMachine together with nginx, can work but I have no expertise with those. At least with node you can't accidentally call a blocking library or make use of the native blocking libraries since JavaScript has no native IO.
Creating a real time website using PHP