Yeah, it sounds like cable cast-on. Interesting that you consider it stretchy, Sean – from what I’ve read (and from my own experience), it’s a fairly firm and inelastic cast-on – good for buttonholes and such. (It all depends on the knitter, I suppose.) I wouldn’t use it for casting on a lot of stitches unless I needed a really sturdy edge. I generally reserve it for times when I need to cast on additional stitches in an already established piece – like when making buttonholes. (It’s also neater than long-tail in that situation since you don’t need another length of yarn to do it.) The reason most people use long-tail most of the time because it works well for most applications, and is quick and easy. Stretchy too, if you do as Amy suggests, and work with a larger needle than what you plan to use in the rest of the piece. (I suppose you could use larger needles to make other cast-ons looser too, now that I think about it.)
ETA: I just did a little research, and there seems to be little agreement on whether or not this cast-on is stretchy. Yeas and nays both ways. I’m sure it depends a lot on how loosely you work.