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.