Traditionally the GSS is a marketing event with real discounts mainly found in the fashion and luxury goods. If you are looking for food, IT or electronic products, the discounts are not significant as there are promotions for these product all year round. You have better luck for IT and Electronic products if you plan your visit to coincident with the quaterly IT/PC Shows.
As a sign that the GSS has lost its relevance, a 2012 Straits Times reported that many retailers were giving the national event a miss on its first day and out of the 275 stores at the luxury mall Marina Bay Sands, for example, only 32 were participating. Another 112 will be holding promotions during the eight-week period, but do not want to be associated with the event. The remaining stores - which include Ralph Lauren and Hermes - said they will not be having a sale at all during the May 25 to July 22 GSS period.
Visit the GSS official website here.