The previous post on dow.ngra.de generated tons of traffic. That tons of traffic generated 120 000 requests to a style sheet file that did not exist. WordPress will display a semi fancy page for 404 files that weighs about 25 KB. 25 KB times 120 000 is 3 000 000 KB :).
Actually the same happened to favicon.ico and a few others. So either have your referred files and favicon.ico on your server or rework WordPress mod_rewrite configuration not to handle css/js/ico/png/gif/jpg files. This will save you money!