We're hard at work trying to get a good skin guide available. It's starting to come along.
Here is what we have done so far:
http://www.windowblinds.net/skinning
The UIS2 tutorial is complete in there as well. For UIS1 (the new language in WB 3.1) I tend to just convert UIS2 skins to it that were made with the knowledge of UIS1's limitations (UIS1 is faster and more compatible but more limited than UIS2 which is the skin language most WB skins use).
If you have any questions about it, post here.
