>> the console is WAY faster with this kernel thanks, moreover there is
>> not garbage on the screen when I exit X ,unfortunately X does still
>> not work :(
>
> So that's another case of Machfb Does The Right Thing Where X Screws Up
> :/

I've been having fun with a G3 All-in-one and NetBSD over the last 
couple weeks. The new kernel with MachFB (finally!) displays a working 
console with color. The old text OF console had weird shadowing (bright 
line to the left of all black). When I run X with any resolution other 
than 640x480x8 at 60 Hz, 31.5 kHz (i.e. the VGA mode at which we're 
already running), the shadowing reappears and the colors go screwy. 
It's probably a similar problem to the iMac issue -- did you try this 
mode?
-Nathan