I also ran into the same problem. I have a laptop and since the upgrade from 11.04 to 11.10 I find it very difficult to move windows around my desktop.
Not sure if it is a bug, though, due to the fact that it works as described in post #8, i.e. do not lift finger after second tap, but rather immediately start dragging the object that you wish to move. However, double tap dragging, in this case, would not be an appropriate name anymore, due to the fact that the second tap is technically no longer a tap.