If you are one of the lucky ones to have a large enough space for double islands, why not consider it! I am currently working with someone that has this opportunity, and we are finding the layout we have settled on will work amazingly for their family. 

Typically I concentrate on small space challenges, but there are actually large space challenges to consider as well. In a large kitchen you want to be sure the work triangle still works with not too many steps, and that the island, or islands, are utilised wisely for flow of traffic and the cooks.

Double Island Examples