If the GM wants to invalidate the Evasion ability for an encounter, he should use spells that use Fort, Will or No Save, or non-damaging Ref's. Otherwise you run into a situation like this:
GM: Your ability works this way.
P1: Okay, I use it that way,
GM: Oooh, sorry, doesn't work that way.
Evasion (and Imp Evas) can be frustrating to a GM, especially if he feels he's supposed to be causing damage. But there are so many other tricks in the bag, that ultimately a rogue being immune to fireball really isn't that big of a deal.
GM: Your ability works this way.
P1: Okay, I use it that way,
GM: Oooh, sorry, doesn't work that way.
Evasion (and Imp Evas) can be frustrating to a GM, especially if he feels he's supposed to be causing damage. But there are so many other tricks in the bag, that ultimately a rogue being immune to fireball really isn't that big of a deal.