It's one of the Google Labs experiments (that went live in mid-March), but anyone can have a play. It returns results to you based on general web popularity, but also browsing history and what you & friends (Google contacts, or via 3rd party sites like Facebook & Twitter if you've linked them to your Google account) are sharing on t'internet.
There are definitely similarities with Stumbleupon , but Play only gives you pictures, text or videos rather than full web pages.
To close, I have no idea why Google Reader Play is finding me things like this!!
