I subscribe to the Zappos' e-mail digest and the following is a great post from it:
From: Justine W.
Subject: Recycling Crocs
I've worn down the treads on my beloved Crocs, so I called the
company to ask if they're recyclable. Customer Service told me that
they will recycle them if you mail them to the company.
Specifically, they're shredded to make padding for children's
playgrounds. Unfortunately, municipal recycling programs don't
recycle Crocs at this time. The company is working on a more
expanded recycling program, but they have not released any details
Since Crocs are lightweight, I estimate that postage will be around
$2. If you do want to recycle your Crocs, clearly mark the outside
of the package with "RECYCLE" and mail them to:
1510 Nelson Rd.
Longmont, CO 80501
(I don't work for Crocs. I'm simply a recycling advocate!)
So if you have some worn down Crocs and you'd like to recycle them, you now know where to send 'em!