I'm using Feza's "Fanatic", in Proscribed Colors (thank heavens I found chocolate-and-turqouise yarn!). It's a bit thicker than called for, so I'm using larger needles and adjusting (following the XS instructions for my XL frame, with modifications to make the pieces fit), and it's flying. I got the entire back finished in one day. I was worried, since it's for my sister's wedding, which is sooner than I'd like, but I'm not worried about the time.
I'm worried because I have exactly enough yarn, and if you ever read the Yarn Harlot's blog, you've heard about what a disaster will befall anyone who doesn't get that extra ball of yarn when they have a chance. (I'll be calling my LNS today to see if they've got another bag hidden somewhere!)