Aren't games ment to be challenging? If you put some overpowered skills in them you take away the challenge IMO. And as Flixerflax said some players can't resist the urge to use those overpowered skills when it gets a little harder(I'm one of those players :p)

If I would have noticed how overpowered scorpions are in Divine Divinity during my first play-through, it would have totally ruined my gaming experience cause I would just have used Scorpions whenever it got hard. Happily I didn't understand I had to use those traps with the Deadly Gift skill back then.

If they would put overpowered skills in the game, please make them hard to get so casual players don't accidently stumble upon them.
Overpowered skills can be fun when you've finished the game or when the game starts to get boring, but when you're playing the game for the first time and you know that whenever it gets hard, you got this 'uber-skill' to just take care of your enemies kinda ruines the game experience for me.

[Linked Image from miniprofile.xfire.com]