To make the whole thing quantifiable in some way, I found a site from the Australian Government which claims that:

“At least 16 US states-including Massachusetts, New York and Rhode Island – have passed laws requiring six-pack holders be biodegradable (these are marked by a small diamond between the rings). Pepsi for example, has a policy to purchase only photodegradable plastic sixpack rings. It should be noted that photodegradable plastics are not a complete solution in themselves as they require 6-8 weeks of sunlight to degrade and will not degrade if buried.” (Emphasis mine)

This may end up being a long experiment!