I have recently started playing a necro, but have been previously playing SK's... this is what I personally have noticed:
1) In my time playing SK's, I have found Dex to be more than benificial in casting than people give credit. Yes, it DOES seem to help reduce interruptions.
2) Dex ALSO makes an item with an effect proc alot more... take a Dark Reaver, for instance. The only reason I even use one is to get the nice siphon. With lower Dex I would go through about 2 to 3 fights before a proc. Once I got my Dex higher (only by 30 points!!!) it will almost always proc within the first half of a fight.
3) Negative Charisma DOES seem to help my fears sticking... I have an Iksar Pariah Mask (5ac, -25cha) and have taken it off several times and HAVE noticed a change... as well as putting all my +charisma items on and trying it. The difference between 25 charisma and 95 charisma was awesome, which brings me to:
4) I have noticed that the low charisma also seems to help my SK land his Darkness spells more often than the higher charisma. One thing that I have noticed with my necro is that his Darkness doesn't land NEAR as frequently as my SK... so I ran around until I found a rotting Iksar Pariah Mask (they are no-drop) and covered my scaley face with it... I don't seem to have near as many resists on Darkness now, as well as the fact that my fear-kiting abilities have seemed to have risen immensly!
Yes, I am trying to get these for my necro, while getting an easy blue bubble out of only 3 kills in Dalnir... and I am soloing (hit 37 2 nights ago in here!) DON"T KNOCK THE DEX AND NEGATIVE CHARISMA FOR NECROS! Try it for yourself... and NO, you probably WONT notice any significant change from only a 5 charisma difference... which seems to be how people conduct their tests. Get the mask and try it like I did.