Just today, Google has added a new entry -- "/chart?" -- into their robots.txt file. Amidst all of the buzz around their free analytics software (previously Urchin), they have quietly changed their robots.txt file -- which generally means they are going to do something with the specified subdirectory.
This change may have something to do with Google Analytics, which they just made available. But could it mean something different? Google has not registered any new domains that contain the word "chart," so the only thing we can do is have some fun and speculate.
What kind of chart could this subdirectory be referencing? One interesting idea might be that they are planning ahead to a music offering. A "top 40 chart" would fit into the /chart directory. A music service is probably not far off since they do own the domain googlemusic.com already.
You have to realize, too, that this robots.txt file isn't strictly for www.google.com. The same robots.txt file can be seen using other subdomains such as mail.google.com/robots.txt, images.google.com/robots.txt, and more. That said, this same file could be used for something like music.google.com/robots.txt. Wouldn't it make sense to see something like http://music.google.com/chart?
Stock "charts" are another example of what this could be used for. If you notice, the entry in the robots.txt file has a question mark at the end -- that generally signifies that you will be able to add extra parameters to the end of the URL. For example, http://stock.google.com/chart?q=GOOG might show you stock information for Google. Another domain that somewhat confirms their interest in the stock market would be googlestock.com which has been registered to them since July.
"Pie charts" or any other type of graphical representation of data may also fall under this subdirectory, however if it was relevant to Google Analytics, wouldn't the entry more likely be "/analytics/chart?" or even an entry in "http://www.google-analytics.com/robots.txt"?
What do you think this subdirectory could mean?