I'm in the process of making it- using acrylic yarn (worsted 4ply or something like that...I'm willy-nilly when it comes to yarns).
I followed the directions for "medium"- it seems to be a larger sizing that I expected. I'm a size 5/6 but the crotch turned out really wide so it looks like a diaper. Plus the cups are long, extending from underneath the boob to the collarbone.
I can't say for certain whether that's due to the pattern or my mediocre crocheting skills!