Calibrate your PID settings -- M303 and the like. There's a handful of guides on how to use it.

http://reprap.org/wiki/PID_Tuning

Save to the firmware with M500 when you've got the new values entered.

Dale - I call that printer roulette. I lose about as often as I win; my current record is 9 3/8", from 6/27. Though that's only since I've been recording them - I'm pretty sure I've had far lower X) perbear - it's not a common issue, but I do like that solution - I had been thinking of an optical s...

Requesting sticky

EVERY Allen wrench I own is in a big pile for some reason. I want to separate out the ones used on the M2 -- which ones should I set aside?

This was right after a firmware flash and some new slic3r settings. My acceleration was still very high (3000), so the bed was probably ringing somewhat, and I didn't have Z-hop enabled. Maybe a more reasonable accel (1200) + Z-hop + keeping the second extruder hot to melt through things is the way ...

This apparently happened towards the end of a 6" tall print. I had no idea PLA was that strong (it was kind of a thin print). Not sure why it took that long to finally catch on the print ... everything before that was perfectly fine.

Guys, ABS cement is a premade (black) slurry of acetone + MEK + ABS. It's used for joining pipes together. It will actually fill in the cracks and solvent-weld everything at the same time. mhorton, if you break yours trying to fix it, I'll print you one for the cost of shipping, if MG won't replace ...

Glue the cracked one back together with ABS cement, and get printing some replacements

That's "raft". Are you using slic3r? It's a setting called "Raft Layers" in the support tab. Make sure it's set to 0.

It will very likely have the V3B extruder, which to be honest is still a great extruder. The dual-extrusion kit is still in beta as far as I know.