I do use nginx. This uses a "Simplish HTTP Push Relay Protocol". It's a way for your app (via curl or any other http library) to "connect" to your http clients.

It has a few interesting options. "messages" are passed by a "channel id" and you can have any number of long polling listeners on a channel, or you can error out the first or last connections on a channel so there is only one listener at a time. If you have multiple listeners the message becomes a broadcast.

You also have a configurable amount of memory to buffer messages in the event there is no listener on a channel, or the listener is busy (receiving a message I guess). You can also set limits on number of messages per channel and a timeout.

I can see the advantages of this easily. The connections in nginx are much less resource intensive then a rails or php fast-cgi. You'll end up using much less ram. I know python has twisted and there are few others webservers for other languages, but this would allow me to run a php based chat server and take advantage of long polling.

I like it.

The nginx module is ideal for heavy frameworks like rails, so that you can handle clients waiting for chat messages (for example) on the web server, and not by the heavy framework dispatchers.