After trying to make a few compartment trays for resistors, I had a problem where there was a resonance in the Y axis which caused waves to appear in the plastic. This happened on the base layer on a used blue-tape surface and caused the plastic to get caught up.
I took this occasion to upgrade the MakerBot TOM with a “Ball bearing mounted Y belt pully and belt tensioner”
It does require a few small holes to be drilled, and a few bits of hardware, but oh, what a difference. See the before and after pix.
(edit 10/3/11 – the additional culprit to the printing problem was that the ball-bearing X-axis mount had dropped it’s nuts, making the print surface wobble a bit).