I have been using ML (currently)2011Jan30.550d.fw109 while shooting a documentary I have been working on for the last couple months. The last date I shot 2/19 I encountered error 70's on my second card. I think most of the times this happened I was trying to do a fast start and shoot where I would power on the camera and hit REC right away. Each time it happened I was able to eventually shut the camera off, pull the batter, restart, and shoot again on the same card. It was frustrating because in each instance I was trying to power up fact to catch breaking action.
The way I have prepared my 5 16GB cards is to adjust one cards ML settings and save it. Copy that cards files to my Mac. Erase (not format) the bootable cards from my Mac and recopy the ML files with saved settings.
I shot plenty of times on the card I was having this issue on with no problems. Of the 16 MOV files I am guess I had about four Error 70 issues.