I think there are a couple of broken or useless skills--true shot, using the wrong sight skill--but most skills are a matter of what fits into your game. For example, I considered limbs of lead invaluable--it works on even the highest level monsters, and is perfect for the person who likes, or needs, to fight from a distance.
Someone else finds evade traps useless. Well if your hit points are low, traps are one of the only things in the game that can kill you outright. A valuable skill if you are trying to play for no reloads with a low hitpoint character.
Someone else find pickpocket useless. Almost, but there are two tasks that can only be completed with this skill. If you are an absolute completist, you need the skill.
I suspect most skills are a matter of how they fit your style, rather than being "useless". Of course the ultimate power gamer might find a set of most powerful skill combinations. But why be a powergamer in <img src="/ubbthreads/images/graemlins/div.gif" alt="" />? The game just isn't that hard, and can be won with an enormous variety of characters.
