This is a good discussion - worth more attention, I'd say. My own feeling is that serving a mobile site on a dedicated hostname is not what the original W3C vision was. Their idea is to serve different CSS files based on the user-agent.
That would certainly make any redirect questions irrelevant. But I can't get past the idea that even with serving an appropriate CSS for mobile browser file, you'd still be serving a lot of unneeded code to a mobile browser. With mobile connectivity and bandwidth challenges very much with us, I'm still more comfortable with a dedicated hostname and a redirect.
Google assures us that a 301 redirect for mobile user agents is what they will deal with most effectively, and I haven't heard any contrary reports.