So yes, they do wear out, however the P/EC performance has been increasing due to improvements in technology, and technically a flash chip is considered safer: so long as the user doesn’t try to push it by doing writes near the end of its life cycle, the non-volatile memory should hold its contents for a long time. A hard disk drive, by contrast, destroys some or all of its data when it fails, or simply due to age (flaking magnetic substrate).

Formatting typically does not erase the contents of storage, but instead writes an empty directory entry and file allocation table. The data outside of these areas is left intact. If you want the data to be completely wiped, you must zero-out the device. I don’t suggest doing that on a flash drive because this negates one of the advantages of the device over an EEPROM, and unnecessarily expends P/E cycles.

The only data loss I’ve experienced with flash cards was due to formatting the device on a PC instead of in-camera. This is due to slipshod programming by camera firmware developers, and there’s really nothing we can do about it other than what you’ve suggested.