According to the universal monster rules, incorporeal creatures (read: ghosts) have no Strength score:
[An incorporeal creature] has no Strength score, so its Dexterity modifier applies to its melee attacks, ranged attacks, and CMB.
The ghost touch special ability allows a piece of armor to both function properly when being struck by an incorporeal creature, and to be "picked up, moved, and worn by corporeal and incorporeal creatures alike."
However, armor still has weight, and all incorporeal creatures have an encumbrance limit of 0 due to their lack of a Strength score.
Does this mean that it's actually impossible for a ghost to wear ghost touch armor even if it's technically able put it on?
Best Answer
Consider that creatures wearing ghost touch armor "can still pass freely through solid objects."
Consider that "incorporeal creatures have no weight."
It seems pretty clear that, narratively, the armor itself becomes incorporeal when worn by a ghost, and thus has no weight.
Regardless, the magic armor has an ability that lets it be worn by incorporeal creatures. If the general rules for incorporeal creatures seem to make that impossible, then this ability, specifically designed for incorporeal creatures, obviously trumps that! :)