Flash memory usually allow about 10'000 write operations. The EEPROM allows about 100'000 write cycles till it gets unreliable. An SD card has the same restrictions but there you have an intelligent controller on the card reordering the write operations in a way that the blocks written to change in every write operation. This way you can use an SD card more like a hard drive but the limitations still apply.
If your project includes an RTC use the nonvolatile RAM they offer because that memory area can be written as many times as you like.