Google is all about numbers, metrics and stats, so it's natural to see features that explore trends in user's activities. There's a product for search trends, one for music trends and now a product that shows trends in Google Checkout.
"Google Checkout Trends aggregates the sales data of Google Checkout merchants and charts it in a matter of seconds," explains the product's blog. As usually, Google doesn't show actual numbers, just the revenue evolution over time. The charts are borrowed from Google Finance, so they'll look familiar.