For example, here's Econista's take on Natalie Portman's vegan shoe line.
Recently Natalie Portman appeared on Bravo's Project Runway hocking her vegan shoe line Te Cesan. While her shoes are adorable, I personally don't think certain vegan shoes are sustainable. Pleather isn't sustainable, in fact it's the opposite. With the exception of recycled plastic pleathers, these materials are made from petroleum products.
The desire to end the suffering of animals is noble and necessary. But plastic is not the answer. Leather is a byproduct of the food industry and using all of the animal does more justice to their sacrifice than letting things go to waste.
Truly sustainable shoes are ones that use recycled materials and use responsibly tanned leathers and sustainable production practices (that's more than just recycled packaging...a message to some of the vegan footwear makers).