I consider myself an experienced knitter. I have been doing it for over ten years now. I like cabling, know various stitch patterns and have done limited lace work. So I was surprised to find out that I’ve been purling incorrectly this whole time. I think this comes from teaching myself to knit in the pre-youtube age. I thought purling was just pulling the yarn through the back of the knit stitch. Apparently not. That is how you twist the stitches. Purling is a little more complicated than that. You actually have to wind the yarn around the needle and then pull it through the loop.
http://www.youtube.com/watch?v=MAMD_XpybQY
But I know none of you out there have this problem. We all have the internet and we all know youtube is a knitter’s best friend.
Knitwerks 
My eldest son started knitting recently and had been doing very well for a couple of weeks. Then I happened to see how he was purling, and he was twisting the stitches too 😉 When I showed him the right way, he was most surprised. He’d tried to learn from a web site that only had drawings and text, not videos 😉