It occured to me recentlty that the use of child themes is perfect for mobile web development within wordpress. You can start off with a base level theme and then build upon it layers of complexity and features.

e.g.

first theme

base theme, limited css styling, written in xhtml-mp

second theme, some javascript, different size images e.g. logos, background images etc. probably still written in xhtml-mp

third theme, written in html5 heavy use of css3 use of javascript larger images.

This would cut dev time as each theme is just progrewssivly enhanced instead of rebuilt and ensure that there is more consistency with themes. I am unsure of the page load ramifications as yet but I will work on that.

This combined with my upcoming and still very much in development WordPress mobile plugin and you can have a framework for mobile to desktop development up and running very quickly.

I am in the process of demoing this with a full child theme. More details to follow.