Icelandic Sheepdogs are AWESOME! I had no idea they weren't a registered breed in the US. They're absolutely adorable, and pretty much have the same personality as collies (duh. Sheep/herding dogs...).
Leonbergers are huge fluffy teddybears. That's all I know... and I've never actually met a Corso.
I own a Dalmatian and a Chihuahua myself - but speaking of chihuahua, there's been a lot of controversy about the color merle and the gene that causes it... while it's allowed in the AKC, the Danish equivalent still doesn't acknowledge it as an acceptable color, and thus, merles aren't "allowed" to breed (meaning their puppies won't be pedigree).
It causes no defects (any known defects have been caused by poor lineage, which would be an issue with all colors) - and still, they allow white, which causes deafness, and their excuse isn't even that there's a problem with the gene either - they're sure it's introduced by another breed, thus, ruining the "purity" of the chihuahua breed.