My makerbot's printing! First print jobs were the engagement ring and the whistle. Thingverse has G-code for both, so I could print them directly without having to run Skeinforge to turn the 3D shapes into extruder lines.
My biggest problem was figuring out the starting setup before printing each. The startup code is in the G-code, not in the ReplicatorG program, so each has a different expectation of where the extruder tip should be. The whistle expected the extruder to be at 0,0,0, barely touching the build platform, while the ring expected the extruder to be 10 mm above the platform (I think). I crashed the extruder into the build platform a couple times trying to get this right.
I also found that the raft won't stick to the build platform unless it's really close, so as soon as the raft started printing, I adjusted its height by turning the Z axis pulleys.
The whistle came out beautifully (and it works!) The ring missed a few layers, and my model wasn't solid so it wasn't quite ring-like enough for me. Still, that's two successful prints!