I would never leave the paint on the face of a BB, steel or not. It can foul up the alignment of the BB shell face to the BB cup threads. Just tightening the BB cups can peel the paint off. It's just one of the problems with steel. It can rust anywhere the paint inevitably comes off - like the dropouts. I'd grease the face to minimize corrosion.

The VO threadless BB is not at all like the MAVIC- it does not rely on a chamfered edge to securely engage the BB shell. It doesn't rely on a knurled shoulder to engage the BB shell like the low end YST BB either. It's an internally expanding wedge shim, made of aluminum, to secure the BB shell. It's pretty damn cool. The colors? Well, they are the same as the French flag.....
A writeup from Moscaline Blog is here:
http://tsaleh.blogspot.com/2010/01/r...hreadless.html
To tie it into this thread, a faced BB shell is a nice thing to have for any BB. It's less necessary with cheaper cartridge BB's like the Shimano UN54 and UN73 (and it's predecessors) where the cartridge is always square to the spindle. A faced BB shell allows the cartridge to be threaded more securely, without loosening up. At the factory level you can do with less precision machining, saving time and money. In most cases a mid to low end production road or mtn bike frame is welded or brazed without much attention paid to the face of a BB shell these days, as there is an expectation of specing a cartridge BB on it. When most bikes were using cup and cone BB's and the left and right sides were entirely separate, a faced BB was much more important to get proper alignment so the bearings would not bind, then pit, the spindle and cups at the tight spots.

Newer outboard bearing designs (and BB's with sealed bearings like the IRD, Race Face, FSA and VO BB's) with an alloy(or carbon or steel or whatever material) spacer benefit from a faced shell though. Because the threaded 'cups' are separate from the spindle, a cup that is slightly misaligned during final tightening may bind the bearings, causing a the spindle to not spin as freely as it could.