I use Ultimate Unwrap www.unwrap3d.com . It isreally good, although I think it could do with a few improvements. The free version (Lithunwrap) is quite good too http://files.seriouszone.com/download.php?fileid=198 . I opened the Carrara UV Mapper a few times and realised very quickly that it was not upto the task of mapping serious models. I rarely touch it. I think it is definately one of the things that needs a serious overhaul for version 4.