Maybe a strange way of using Carrara. A client discovered that two foto's of dishwashing machines had their perspective off, he wanted them the same (the perspective was changed because of a dent in the machine that would be too noticable).

I used Vanishing Point in Photoshop CS3 Extended to put a simple box in the right perspective around the machine. Export as 3ds file, import in Carrara, slightly change the perspective to match the reference photo and, voila!

For background material like buildings etc. the new Vanishing Point can be a quick way to extract material from photos that can appear in 3D, with some limitations of course.