Upon joining SubmitHub, there's a good chance that you'll start receiving demo submissions straight away. As you know, demos can pile up very quickly, so SubmitHub is best treated as a replacement rather than an additional source of submissions.
At Indie Shuffle, for example, we no longer accept submissions from any other source except SubmitHub. Instead, we use an auto-responder on our email address to tell people that they can visit SubmitHub to share music with us. Eliminating email submissions has been a huge relief on our workload, and allows us to focus first-and-foremost on the song :)