It's always interesting to share different views.. I'm quite sure that in Italy this was more related to a nonsense old religious habit,rather than a matter of bad luck like in China. Decades ago the left hand was considered "unclean" a.k.a. Lucifer's hand. I prefer to write with my left hand, even if sometimes I switch automatically to the right one. This was useful when I was studying at University and Professors made us write like crazy ants. When one hand was tired, I wrote with the other one.... And while skating I basically did the same with jumps and spins..
Treesprite: I've never practised mirror writing, but I'm quite comfortable writing and reading backwards ( definitely saved me during Latin classes when I had to translate and I hadn't studied... And the teacher kept his book open without thinking I could read..)