Which great class ability do you dislike?

I agree, there's no significant advantage, and most importantly, it clutters the skill slots with various useless things like summoning magic (which I think is terrible) and forces you to sacrifice such great abilities as mass haste...
But, admit it, getting all the spells and being able to cast them at the expert level is really cool!
By the way, I've never leveled up this ability; does it happen to grant mass spells as well? If it does, then it's definitely the best, and all other abilities can go to the trash!