For theme creators using ThemePark and ShapeShifter, previewing your theme while you're working on it sucks in the same way that accidentally smashing your nuts while using that mallet to drive fenceposts is "sort of a bummer".

ThemePark's built-in preview is pretty lackluster. It's basically the equivalent of just replacing the Extras.rsrc file manually (although it follows the ShapeShifter ideology of not touching any files inside of /System, so that's not actually how it works). This means that you don't get the benefit of any of the special mojo that ShapeShifter does to make your themes live and breathe, and the more advanced ShapeShifter becomes, the more apparent this limitation becomes.

Verdict: Previewing your in-progress theme in ThemePark is nothing more than a best guess estimate of how things'll look. Teh sucki.

Previewing in ShapeShifter is great - the preview is exactly what you'll get when you actually apply the theme. But it's a pain in the ass if you're a theme creator - you need to get rid of the version that's already in ShapeShifter, export the theme from ThemePark, drag it into ShapeShifter, then preview it.

You'll probably get sick of this really fast, and no theme will get made, robbing the world of that special something that makes you you!

Verdict: Better, but hampered by "pain-in-the-ass"itis.

As of ShapeShifter 2.4b3, there's a nice solution for this. These betas completely revamped the internals of how themes on disc are syncronized with what you see in the SS prefpane, with the result that what you see in the prefpane is now a live rendition of what's in ShapeShifter's theme folder.

The upshot is that you can just leave the ShapeShifter prefpane open while you're working on your theme in ThemePark. When you're ready to preview, export your theme directly into <your home directory>/Library/Application Support/ShapeShifter guiKits, replacing the existing build if necessary, and BOOM, you'll see the little progress indicator suddenly appear in the SS prefpane and your new build is live, selected (if it was before), and you're ready to hit the preview button.

Verdict: Dropping Panther support felt good!