Google have released a new 'game', whereby in conjunction with a random partner, you agree on labels for random images you're both presented. You basically keep suggesting labels until one matches a suggestion from your partner, and then move onto the next image.
It's nothing too amazing, but it kept me entertained for about half an hour...my top score was 700.
It becomes obvious quite quickly that trying to be too descriptive jut doesn't work, and that the lowest common demoninator is most often the first match (e.g. 'man', 'landscape',' two'), but there is an 'off limits' list, that I assume is stopping you from re-labelling with 'established' words.
http://images.google.com/imagelabeler/
(technical things follow)
From a technical point of view, it's quite an interesting application. It is, as far as I'm aware, the first thing that google have released that uses GWT (Google Web Toolkit)- which basically compiles Java code into Javascript, for running in a browser.
It also runs as a single web-page, with no refreshes, and it is an application for which this actually works- such applications prevent the browser's back-button, and bookmarking from working in their normal manner, but you're not going to want either of these when playing.
It still relies on polling to check what your partner is doing, rather than keeping a single connection open as is becoming the trend, but from a user's point of view it's fairly seamless.