I didn't, actually, we were in a rush and we started building something with socket.io which I guess is (one of) the easiest way to start. And then we had to scale the backend accordingly and it was a pain in the neck.
To be honest, I'm wondering if there's a space for a SAAS product around realtime...
I would think the opposite -- that's it's too popular a space. But I'm still surprised at how many services don't have it and need it, so maybe I'm wrong.