I think this can probably be closed.
Skinning YUI is a difficult task and doing so would not only involve creating a skin based upon the currently used sam skin, but would also mean watching for and maintaining it during YUI upgrades.
On top of that I think really all that we are doing 99% of the time is tweaking the way things look. There is normally a bit of a challenge in writting CSS for YUI components, the biggest being their strange usually not quite enough information docs. But they do think of people altering styles and tricks like the one Marina mentioned (bind styles to a parent with an id) normally do the trick and allow people to style with just the aid of tools like firebug.
+1 from me to close this issue.