Hi UncleCheese!
I'm running the latest checkout of DOM together with the latest checkout of branches/2.4 and started getting errors about livequery not being a function. It's worked before I updated so I'm wondering if something's changed in your code or in theirs?
Anyways the to fix this for me was to make sure that DataObjectManager requires the file in the __construct() function and that DatePickerField requires it in its Field() function (in case DatePickerField gets used on a page that doesn't have the DOM on it).