Tweakie, is there a good collection of the possible causes of missing steps somewhere on a cnc forum ?
Yes indeed, but you could spend all day reading
There are thousands of them here http://www.google.com/cse?cx=.....page=1
And again here http://www.machsupport.com/forum/index.php?action=search2
As mentioned earlier, most of the problems relate to mechanical issues such as tightness or binding of the lead screw / linear slides which show up when an axis is driven too fast (stepper motor torque decreases as rotational speed is increased and there comes a point where the resistance to motion exceeds the available torque).