[Link14716]

Everytime you buy coffee, it could add either a "1" or the type of coffee you bought into a field in the user table. Then, next to your posts, it'd add a little image (probably next to your screen name). If you had it insert the type of coffee into the user table, then it could be the tooltip of the image.

Also, it could be changed (as a mini-addon) to use store money. Of course, the price would need to be changed to $3 and $4 respectively.

After all that, it still really doesn't have a purpose, except for draining your store money (that you can give back to yourself in the admin CP ) on buying a little coffee image to show up next to your screen name. And I don't think it's be that hard to do that either. Maybe a few edits in cafe.php and maybe 1 or 2 edits in functions.php.