I have designed business cards, letterhead, envelopes, forms, posters, booklets, brochures for my printing business with Scribus. To be honest I only use it about 15-20% of the design work probably because I am much more knowledgeable in the Adobe apps since I have been using them since the early 90s. Though the more proficient I seem to get with Scribus, the more I have been using it lately. My biggest complaint would be that the bottom edges of the text boxes cannot be moved up to the bottom edge of the type in the boxes. Next would be tables, though in 1.5 they seem to be coming along, not as great as InDesign, but usable. A wish would be that true black/white bitmaps would import and export as bitmap and not as greyscale available with transparent background instead of the white square background (though this could just be a lack of knowledge on my part). Another wish would be to be able to apply 'spot color monotones and duotones' to greyscale or bitmap images since I print a lot with pantone colors.
Regards,
mnawij