I normally would not report bugs like these but the adCenter blog just posted an official confirmation of the bug I reported early this morning at the Search Engine Roundtable. The bug is that advertisers were being charged astronomical prices per click, even though they have set their bids lower.
One example is an advertiser set a bid price of 50 cents as was charged over $280. There are many other cases, even some of advertisers being charged over a thousand dollars for one click. I suspect, based on the volume of reports at the search marketing forums that this bug has cost advertisers millions of dollars, but I can be wrong on that figure. We do know, based on the adCenter blog post that (1) Microsoft has just fixed the issue and (2) now they are working up a plan to credit all advertisers who have been overcharged during this bug cycle.
Postscript: Microsoft Refunds adCenter Advertisers Over Weekend, so I think Microsoft handled this as well as they could of.