Depende da tecnologia de memória flash, que depende do fabricante. Extraído do "Manual do Produto SanDisk SD Card":
SanDisk SD cards have an endurance specification for each sector of 100,000 writes typical (reading a logical sector is unlimited).
Therefore, extremely heavy use of the card in cellular phones, personal communicators, pagers and voice recorders will use only a fraction of the total endurance over the device’s lifetime. For instance—it would take over 10 years to wear out an area on an SD Card based on a file of any size (from 512 bytes to maximum capacity) being rewritten 3 times per hour, 8 hours a day, 365 days per year.