Cafepress's API does break every now and then. In this case, a corrupt local cache of the javascript was causing the issue.

Clearing the browsers cache and offline storage cleared the problem right up.

Give it a try.

Casey, I'm still having the issue with using the Widget to pull CP products into my store. I think I found where the problem might be coming from though. On my one site the widget wouldn't show on any page that was a product/section page, but if I went to a page that didn't have products (i.e. Customer Service page) they showed up. I then removed the keyword for the widget and it now shows up for almost every single page on my site.