Let me mention a few additional points not really discussed in the article here:
When I'm surfing I will occasionally see people talking about WindowBlinds. Normally it's positive but sometimes it's really really negative. The reason is that those people ran into problems in either stability or performance.
Let me address that issue:
On Windows 98, ME, NT, and 2000, WindowBlinds provides its own skinning engine (wblind.dll). But on Windows XP, it uses uxtheme.dll for much of the work - i.e. on XP, WindowBlinds is a native solution so to speak.
The problem WindowBlinds has traditionally suffered on Windows 98
The Windows 98
So what Stardock has done with WindowBlinds 3 (and it should be quite noticeable -- we hope) is make it a LOT smarter about what it loads. Most programs do not use every single GUI element possible (that is, not every app has scrollbars, radio buttons, tab controls, header controls, etc.). But WindowBlinds 2 would just load the entire skin for each and every app. WindowBlinds 3 doesn't, when the app is loaded, it sees which controls it uses and loads just those. This speeds things up and causes it to use fewer resources as the system goes (this isn't to say that on a freshly booted system with just WIndowBlinds that you'll have more GDI resources free since it only really shows up when you start loading a bunch of apps). So this should make things better for Windows 98
The other note I wanted to make is about the "native" or "real" skins. Some WinXP users have confused .msstyles ("XP visual styles") as being more "native" than WindowBlinds. Their proof is that WindowBlinds required a loaded process.
In fact, .msstyles requires a loaded process too called svchost.exe (one of the myriad of them). I guess if we were smarter we'd rename the WB process to be svchost.exe and voila, we're home free.
A year from now, skin formats will be likely seen as the same thing as graphics formats. Just because Windows 95 came with only the ability to use .BMP files didn't stop people from using .JPG files or .GIF or .TIF or .TGA files. .UIS skins are just as "native" as any other skin format on XP as long as they use the XP APIs to do their thing which is what counts.