This is a script to help you diagnose axis problems without making a dozen oddly sloping 20mm cubes. It homes your machine, defining home as X-57 Y-57 which puts X0 Y0 roughly in the center of the build platform. It then makes several moves all at a set speed. The moves include a big "plus" shape, an "X" move into the corners (this one seems particularly prone to bad resonances) and then two trips around the Carabiner V2 shape cut and pasted from rapids created by Skeinforge's "comb" setting (the second copy is rotated 90 degrees). That particular shape is what made me realize my feed speed was too high (and my Y belt was far too tight).
After its little dance it re-homes the machine, leaving it positioned so that you can go into "Control Panel" ctrl-J and check the "X Position" and "Y Position" under the Jog controls.
I would love to see this done with some big circular moves via G2, but I had trouble with my makerbot following circular moves with uncommanded linear moves that crashed into the side of the machine with no sign of stopping...
Save the script in replicatorg-0023/scripts/calibration/Smooth Axis Test.gcode. When you restart ReplicatorG it will show up under File|Scripts|calibration. Click "build" and watch your machine dance. At the end you will be prompted to open the Control Panel and verify that the machine's X and Y positions are both "-57" (which is what the script set "home" to at startup). If you see some other value then your machine lost steps while dancing.
The default speed is F4000 (4000 mm/min, or 66.66 mm/sec to convert to Skeinforge units). This is the same as the maximum speed set in the control panel, though you can set it faster (and lose even more steps). You can test other speeds by adjusting the marked line in the gcode.
If you are trying to diagnose a tricky issue you can cut and paste all of the "G1" lines (the vast majority of the script) multiple times to repeat the moves.