Trying to select dimensions only, wasn't working, grabbed everything.
Playing with it, it appears that in the select mask window, if I have all types selected and click on Dimension, so that it only is highlighted, it still selects everything. (Going from the state all types selected --> dimension only).
But if I clear the selection before, by clicking on white space below, it works. (Going from the state all types selected --> no types selected --> dimension only).
(using only 2D features at this time)
Mid-2010 Mac Pro, ATI Radeon HD 5870 1024 MB
6 core, 3.33 GHz
32 GByte ram