Peak buffet/AYCE surcharge doesn't usually extend into August. In 2009 it ran from right before Memorial Day (I think May 24) to July 11. No surcharge dates for 2010 can be found online, but look for it to be at least a week around Easter and the end of May - mid-July.
Basic dining plan peak pricing for summer is in effect from June 4 to August 14. The adult basic dining plan will cost either $46.99 or $47.99 (have seen both, don't know which is correct, plan on the higher price) per night per adult, and $12.99 per night per child. This is an increase of $5-$6 per night for adults and $1 per night for children. There is no peak season price change on the quick service or deluxe dining plans and apparently no seasonal increases in basic DDP price for DVC members staying on points.