Last night, I tried it out and it worked well. But this morning, it is not working. I hope to update this post with example searches when it is back and running.
In short, Google Checkout Trends uses Checkout data to show you trends in what people are buying and selling online. It aggregates the sales data from their merchants and plots the revenue (price x quantity sold) over a time chart.
Currently all results return "do not have enough search volume to show graphs."
Forum discussion at Search Engine Watch Forums.