I have not worked with Valve or released a game on Steam, but I attended a talk given by some guys that just released their first indie game on Steam.
I doubt you'll hear much from them if you're in pre-alpha. He said that when they first contacted Valve, they were told not to send screenshots or demos or anything due to legal reasons. They didn't get much attention from Valve until they ignored that and started emailing screenshots and demos anyway (they were near the end of beta). Valve liked what they saw and hooked them up.
From what they said, Valve is very friendly towards indie developers. They said selling on Steam has been a great experience and they made back all their development costs within a month of their game being on sale.
However, he said that they get tons of spam to that email address from people who just have game ideas and not an actual game, so if you are in pre-alpha my guess is you'll get the cold shoulder. They have to filter people out somehow. But go back when you've got a solid beta or a demo and they'll probably welcome you with open arms.