microtype fully supported now by XeLaTeX? If not, how can I keep myself up-to-date on this argument?
As can be seen in the last line,
xetex only supports protrusion.
Some time ago, it was rumoured that font expansion would be added to
xetex, too, but it seems that there haven't been any developments in this area recently.
Tracking (aka letterspacing) can be achieved with
fontspec and its
LetterSpace font feature option.
To stay up to date it should be sufficient to keep your tex system up to date, and for new
microtype versions check the Change history.