Oh nothing really, it's just another cog is all. I'm running nginx because there's some things I want to serve statically (and it does a couple of other boring tasks really well too), so if I could just point it at the environment and tell it to go for it then it would just be a bit less messing around.

I'm connecting nginx to gunicorn through a unix socket too and found that to be a bit of a pain.

I largely agree here that of all the components in a stack, unicorn seems to be the least troublesome and almost invisible.

I have never had a problem that I would have traced back to gunicorn not working ...

On the other hand not having to run gunicorn as another separate service might be an advantage.