Don't all rush to help at once guys! Anyways, I figured it out for myself - I have the mighty styler toolbar installed and it seems that if you switch the theme service off styler will still work but windowblinds won't. If I disable styler and reboot, windowblinds works without the theme service. Incidentally, you can do some really cool things to the explorer toolbar with styler - it'd be cool to be able to do similar stuff in windowblinds don't you think?