It was mentioned in the 3145 thread, but seems to have been snowed under in all the other awesome stuff that's going on there.
Basically, you benefit from the efforts of Ray in creating them (a non-trivial task) and from Patrick's in getting them on the website.
We've got the four main aspect ratio's supported now, which should make it possible for people to support HD screens and mobile phones (with some slight resizing).
Paul