Replaced the standard cupcake threaded rods with trapezoidal rods. It rocks!
I was really unimpressed with the rods that came with my Cupcake package. Most of them were already not very straight and made the Z-stage wobble really bad. Now the z-stage flows really smoothly. Hardest part was to get the ReplicatorG axis scale value right so that the stage moves right amount.
Where did you get the rods and nuts?
I bought them from Wexon in Vantaa. Nuts came with the rods.