I gave this a quick try too, and it looks pretty slick.
I made a pretty wild button with gradients, border, radius etc, and it worked great, except for one item.
I noticed it put this css
outline: #858585 1px solid;
right after the border, and radius.
I have personally never used outline, and wondered why it was used, because it gave the button an outline that was square even though the corners of the button were rounded, so it made the corners look odd.
I also like the option of some other presets like mac, windows etc as I am not a big fan of the standard WA presets either :-)