Overture made some major changes over the weekend. Could that account for it?
Unlike the Phrase and Broad match types, Advanced Match is not bid upon separately from Standard Match. Instead the bid setting for Standard Match is used when the Advanced Match is enabled for a particular keyword. BidRank Upgrade Information
You should check your campaigns carefully. Since the last update I found that "tracking urls" had been mysteriously turned on. Also if you have content match turned on and had bidding lower on those they have been "Automatically" made the same as your other bids. Broad match has now been put in place. You may find that you need to go in and choose some negative keywords for those terms.
Had a similar event occur to us: huge jump in clicks with out changing our position and no noticeable increase in conversions. Contacted overture, their response was “only bid what you can afford to spend”.
We had a huge increase one day last month, and when we contacted Overture, they of course hemmed and hawed. Then it turned out that our keyword had been featured on MSN's home page that day as a "suggested search". There are 5 suggested searches every day, and we were unfortunate enough to be one of them. Overture said they had told MSN not to put any terms on suggested search that were over $1/click. Anyhow, Overture refunded our money.