Since everyone seems to want it, here's a quick hack that lets you view game rank plotted over time. Construct a URL of the form:

http://mkgray.com:8000/cgi/bgg-rank.pl/GAMEID

If you only want the last N days, append "?last=N" to the end of the URL.
If you want to embed the image, append "?embed=1". If you want to do both, append "?last=N&embed=1".

For example, Agricola's ascent in the past 60 days:



Can you spot the date Race for the Galaxy became widely available?:



Or, Carcassonne, since historical ratings were enabled.

It caches the xmlapi request for 12 hours to avoid slamming the server, so be patient when it doesn't seem up to date with the latest minor rankings toggle.

Oh, that's awesome!

Very cool, but I think the Y axis should be inverted.

Yup.

Meh, a graph is a graph. Whatever is easiest for Matt.

And for a load of pre-prepared ones (though not all with the latest data) check out:
http://www.boardgamegeek.com/geeklist/27105
http://www.boardgamegeek.com/geeklist/30888
http://www.boardgamegeek.com/geeklist/33047

link does not work

Yeah, temporary DNS provider suckage. Seems to be better now.

Hm, the graphs are blank for me.

Same here no graph.