Group: current SVN version
In metaball edit buttons (F9), current CVS version has number buttons for Wiresize, Rendersize, and Threshold (2.36 release had sliders). Like normal Blender number buttons, they have little triangle arrows at the left and right edge, meaning you should be able to click on the left or right edge to increment/decrement. It doesn't work for me.
Mac OS X 10.3.8