I have never and I mean NEVER been able to slash dough with anything close to the dexterity I see in videos. No matter how wet or dry the loaf (and I have left loaves out in the dryest of environments to form a skin), what tool I've used (fresh razor blades, serrated knives), or whether I flour the begeesus out of the loaf, oil it, oil the knife, etc, all I end up doing is poking the dough and dragging it off to one side!
The only thing I can think of is that I'm not developing enough tension in the loaf when shaping. Everyone talks about how important shaping is and I'm beginning to suspect this might be my problem. You will see in the video that I'm using a fairly wet straight white dough at 75% hydration and the shape is a bit blousy. I appologize in advance for the shaky video, but I was (attempting to) slash with one hand and video with the other: http://www.qwt.com/downloads/IMG_0089.MOV 
But...I finally figured out the stretch and fold method and the bread was creamy and flavorful with a delicate crisp/chewy crust that didn't score the roof of my mouth. Success comes in small measures!