Actually, the Enemy Skill Materia was one of the few things about FFVII that I thought was better than most of the other FF games. I liked the idea of not having a dedicated Blue Mage -- usually, those characters suck enough to not be worth using them, so they don't learn any enemy abilities to get any better. But with the Materia, you could put it on an otherwise decent character (since they're prettymuch all the same anyway), always keep it in the active party, and it's always there to collect abilities.

So I used it all the time. At least one person in my party would have it equipped.