Ok, here is the hypothetical:
a 7th lvl rogue has both the major magic talent and the Bookish Rogue feat. They also have a spellbook with a few 1st lvl spells in it.
If they took the Empower Spell-like Ability feat, does it apply to any spell in the major magic slot or just one particular spell and if they switch to something else, they can't use the feat until they switch back?
Obviously, we are talking only about spells that could be empowered like shocking grasp or magic missle and for the sake of this discussion, we can assume the character in question can take Empower Spell-like ability even though it is a 'Monster' feat.
Thoughts?
Edit: For what it's worth, I am inclined to think that it's the latter.
Shameless bump.
Only one.. I promise!
I'd say you have to pick just one Spell-like ability to be empowered, based on the feat's wording.