I've been having problems with prints taller than around 2" exhibiting very noticeable lines and layer shifting at irregular intervals. This occurs more frequently and prominently on the left side of the print which is the first in the direction of extrusion of each layer. The effect diminishes on the right side as the nozzle makes it around towards the second half of each perimeter.
Another thing I've noticed which may very well be related is what appears to be poor leveling of the build platform even when calibrated via the suggested guidelines for my printer (Dremel Idea Builder). The process is to use a sheet of paper or a notecard for each of 3 adjustment points. When I do the leveling very carefully and then once more to confirm all points are spaced the same the first layer of my print always exhibits tight spacing between the extrusion lines at the right-rear corner that transition to wider gaps towards the front-left corner. I can only guess this is due to the fact that the right-rear is BETWEEN two adjustment springs and the front-left is on TOP of a single spring...thus having more "give".
I have done a quick test of using a notecard to calibrate the space of the back and front-right points and a sheet of paper for the front-left point. This seems to have made the first layer MUCH more even and perfectly filled. I will run a full size print tonight to see if this indeed reduces my lines issue.
Here are some images that show what I'm talking about. Keep in mind that many of my earlier prints never had these line issues. It's only in the last few weeks they have started to become more problematic.