This is interesting. Would this work if I was on the site for say an hour? Or is there some limit to the amount of time you can send data like this? I have never tried anything like this. What is the overhead like?

I've only used it on smaller projects. Facebook use it on their frontpage for progressive loading (check the source for `<script>big_pipe.onPageletArrive(..);</script>`).

Longer running connections are a little more problematic, but some client side code should be able to handle the connection being closed. You just need to make sure your web server can handle the number of connections your are expecting. Apache is particularly bad for this. Something like nginx should perform better.

Not hard. The client could notice if the connection dies (JQuery has AJAX failure callbacks, for example) and then attempt to reconnect; that's the important thing.

I was going to suggest long polling as well. Seems to make way more sense than normal polling for this application.