I don't see how its possible - what in the hell kind of max bid did you place? My worst experience was on my first ever adwords campaign - didn't set a campaign limit with a WAY over max bid - woke up to a nice 180 dollar total bill (did about $40 in conversions, still a loser).
That really hurts - but they do it for the popularity if i am not wrong, but, still charging this much is rarely seen.
Be very careful with Yahoo. I have had my bids change all by themselves to the maximum. And I have had daily spends exceeded by more that 500%! A tad beyond the 10% allowed. I check every few hours on all my yahoo stuff.
Wow that must have been a slap on the face when you saw it, I guess you got over it, well done would have taken me weeks