Chris Ferdinandi wrote a good summary of the responsive site vs. separate mobile site debate in Content Parity on the Web:
The gentleman I was chatting with mentioned that for mobile users, he intended to share about 50 percent less content and reduce the steps in their checkout process to make it more efficient. I think that’s a great idea, but I don’t think it should be limited to the mobile site.
If 50 percent less information is the right amount of information people need to complete their tasks, then you should only provide that 50 percent on all devices. And if visitors on laptops could use that additional information, why wouldn’t someone on a smaller screen want access to it, too?
Whenever I chat to people about Responsive Web Design, there are always arguments about how users want different information on mobile devices than on desktops. This usually plays into the myth of mobile context, but in some cases, there are legitimately different use cases. In those cases I press on to argue that separate use cases are not proof that you need a separate mobile site, but proof that your Information Architecture needs some additional work to make the right information easily accessible regardless of the device being used.
But we’re still figuring this out, of course — no one has all the answers. Just reading through some of Luke Wroblewski’s notes from BD Conf got my head spinning again. So anyway, if you’re in Cape Town next Thursday and want to argue with me about this stuff in person, I’m doing a talk called Responsive Web Design in Africa — Why it’s time to adapt at the next SPIN gathering. It should be fun.