I can set the ti.ui.defaultunit property in tiapp.xml to 'dip' and have font sizes respect that setting.
I can explicitly set fontSize='14dip' and text will be sized appropriately. But setting the default unit in tiapp.xml and setting fontSize=14 gives px based font sizing.
See the attached screen: <property name="ti.ui.defaultunit" type="string">dip</property> is included in the tiapp.xml file, the field labels (URL, Username, etc.) are set with fontSize=## whereas the contents of the first text field is set with fontSize='14dip'
Tested on my Galaxy Nexus running ICS/4.0.2. I'm using the https://github.com/gshipley/BeerShift application featured in the developer blog.