I've just added my latest tutorial to the Scribus Wiki. It shows how to use some of the image effects in various "artistic" ways. It's by no means comprehensive but it covers a few of the usual things people might want to do with images. If I've missed anything important just tell me (or update the Wiki yourself).
You can find it here: http://wiki.scribus.net/canvas/How_to_be_artistic_with_image_effects