I just found out about this today ... sounds like the right day for that new camera, kayak, backpack, tent, etc. 
All the details are on the Mass DOR Web Site.
A recently enacted statute provides for a Massachusetts “sales tax holiday,” i.e., a single day during which most purchases made by individuals for personal use will not be subject to Massachusetts sales or use taxes. St. 2003, c. 141, §§ 55-59 (“the Act”). The Act provides that the sales tax holiday will occur on August 14, 2004 and on that day, all non-business sales at retail of single items of tangible personal property costing $2,500 or less are exempt from sales and use taxes.
All the details are on the Mass DOR Web Site.