This is so cool!
I just found this nifty little article
about long-tail cast-on that has great pictures showing the two different sides. What's interesting is that she says that she likes using each as the "right side" in different instances -- she likes the purl-side (the one Sue likes) for free-standing edges because it lies flatter, and she likes likes the knit-side (the one I like) for edges that will later be sewn because it's easier to seam. Good to know. She also has a tip for casting on without having to estimate how much tail you need. (You may have seen that one before, but if you haven't, it's a clever idea.)
The one thing I disagree with was her assessment that alternating the knit and purl versions of long-tail cast-on (for ribbing) is difficult and takes a long time. Once you figure it out, it doesn't take any longer than just doing the knit version. The motions are very similar.