I feel like I'm missing something here.  In my document properties (see first image), I've got my linear dimensions text set to center.  However, when I dimension the text is not centered and I have to choose to center it every time.  Am I not seeing the setting for this?

Also, how does the whole 'dragging multiple dimensions' up/down or right/left work?  I tried holding down alt and shift.

Sometimes, after selecting a dim string or group, picking a dim will move them all up or down, but sometimes it won't.  Sometimes that same dim that worked won't work at a later time (see second image).