I'm trying to figure out how to make this type of thing scale beyond your first 100 customers, and I've come up with a few thoughts.
1. Don't create that expectation of a personal connection. This is the most common thing you see at large companies. I don't think this is a good way to do it.
2. Hire someone as the face of the company -- the community manager probably, and send a mix of automated and personal mail from them. But make them the face of the company. This is something I'm responsible for now. And it still has limits.
3. Randomly assign a contact person within the company for every signup. And automate the insertion of their signature in every email. This however has issues with turnover, and the voice of the emails.
So far, I think what works best is automated (but specific) emails from me, the CEO. And then introductions to the rest of the team for problem resolution.
I'd love to hear what others think works best.