This question was addressed by jack and Suzy Welch. Reference Mint, Campaign, 10 Dec 2007, Page C8
They say material adverse change clause is being invoked by buyers due to the credit constraints they are facing now. The MAC clause is vaguely worded and they emphasize on CEO taking interest in the contract till the last word rather than leaving it to lawyers. When stakes are high, you have no choice but to be there till the end.
Possible litigations mentioned:
Sallie Mae, Inc. vs. JC Flowers & Co., PE firm
United Rentals vs. Cerberus capital management, PE firm