Seth Godin blogged today about emails that explicitly say, "Do not reply to this email. Here's his take.
Email is a unique medium in that it can be personalized and allows for instant feedback. Seeing that note at the bottom is a pet peeve of mine. I shared my address with them and indicated that I was open to their messages, I think the least they could do would be reciprocate and have an open line of communication!
For transactional emails, I can understand this. And, as Seth points out, larger companies may not be expected to sift through the one-off responses that emails could generate.
But, for smaller companies, having a dedicated reply-to address for emails is imperative. It's a step email newbies are likely to forget. But in doing so, they're missing an opportunity to have human-to-human interaction with their customers. Ones that want to hear from them, no less!