Okay, I thought I was smart and instead of wrapping my yarn into a ball and working from that, I found the center of my yarn skein and went to town…which worked great until it started knotting. Three skeins, two have knotted to the point that I had to cut the yarn. Am I missing something here? How can I ever use the center pull if it always knots? 
[size=2]edit - [color=violet]mod squad was here[/color][/size]
Mine knots pretty often, too. I just ask my dad to fix it. 
Some yarns pull from the center without a problem, others have knots. I guess that is why some people rewind all their yarn before they use it. I think it really depends on the brand and type of yarn.
My problems with pulling from the centre are hit and miss… even within the same brand. Sometimes I think it has to do with how I’ve reached in to grab the middle and yank it out. When I get a tangled blob of yarn, I usually try to gently coax it and get it untangled, rather than pulling on it and making it an inpenetrable {sp?} mess.
Also, some brands need to be pulled from a certain side…don’t know why. If that is the case, it should say on the label which side to pull from.
When I first started knitting and crocheting I didn’t know you were supposed to pull from the center, I have always taken the yarn from the outside of the skein and rarely had a problem. I have only wound a few skeins into balls and the ones I did it was usually because I would get a tangle towards the end of it because the yarn was getting loose and winding it prevented it from becoming a huge mess.