Hi,
...snip...
> OTOH the OLPC XO's unique display has no sub-pixels, so we do not 
> actually want sub-pixel rendering. It's good to include nonetheless,  but 
> we need to make sure not to accidentally enable it when running on  the 
> XO, or if display scaling is enabled.

Good point.

In addition to the BitBlt VM changes, the sub-pixel anti-aliasing also 
requires the optional FreeType Plus (sub-pixel anti-aliasing) package to be 
loaded.
(that is FreeTypeSubPixelAntiAliasing-tween.3.mcz , or later). As long as 
this package is not loaded, sub-pixel anti-aliasing will never happen.

However the BitBlt changes also give gamma / contrast adjustment, which 
might be useful on the XO's display.
I am guessing here, but it is possible that using different contrast 
settings for monochrome and colour modes may give good results.

I got to see an XO machine , for the first time, last Saturday and fell in 
love with it.
It's the flip up 'ears' that do it for me, so cute :)

Cheers,
Andy