well i got my copy finally
i was expecting live previews/mockups like the old TGSoft StyleBuilder for XP, but no such luck. fortunately it's got an in-memory uxtheme patcher built in, so it's dead easy to apply changes and see how it looks.
the layout is a bit overwhelming, it's going to take some time to get used to where things are, fortunately, it's possible to search for elements in a variety of ways, including by the resource number of the actual image inside the .msstyles file.
overall it's quite nice, and it's going to make building styles a whole lot easier. you can assign an external editor, so you just hit a button and send the image out. edit, save, then go back to Style Builder and click OK - it imports it immediately. i guess it uses a temp directory someplace... easy!
you can even edit parts of images - just export the hover or pressed or inactive parts of a button for example - and the app will re-assemble things for you.
not tried to import Vista styles yet - no time, i'll try later today and report back.
overall i'd say it's definitely a good investment for anyone interested in making visual styles for 7!