I completely agree with you. Given the wide variety of device sizes that we have to consider, responsive themes are the best solution. Just a bit of a learning curve, and certain limitations to keep in mind.
I am using TwentyEleven on http://72.47.210.126/ , http://72.47.209.96/ and http://theintuitivecompass.com/book/ , three closely related websites. My websites tend to have highly customized looks. As you resize the sites above, you will see that elements start overlapping and that the navigation on the left becomes a problem. Figuring all of that out will go into the next phase of development.
I also did some experimenting on http://drron.me. You will see that resizing works well here even though it is also highly customized.
Have you used TwentyEleven for any of your sites? Were you able to customize it the way you wanted?