I honestly didn't know it was still actively being developed. It has long been surpassed by other options, but I do have some [mostly] found memories of working with YUI. In the early days it was a lot more feature packed than most other frameworks I tried. In the first big professional project I helped build some 7 or 8 years ago, I even fought to use YUI over jQuery. Maybe its time to send a mia culpa over to my old company...