One problem being, that most of the 'SanDisk' product on eBay and in discount stores is knock-off product from Chinese forgers, and will not be SanDisk quality, or warranty.
Point: Every flash card will die. The flash memory chips have a finite number of read/write cycles they can do. So
1) Never use flash memory for active files - that is, ALWAYS copy the file onto your hard drive first, work on it there, and then copy the finished result back to the flash memory, if you need to transport it. Opening a file directly from the flash drive will shorten the life of the drive or card dramatically as temp files and iterative saves are made to the flash chips.
2) Assume at any time the flash memory will fail - always back the files up onto other media as fast as you can.
3) if it starts being flakey, reformat it once and treat it with suspicion. If it gives any other trouble - throw it away. It's not worth the time and cost of recovery, or the lost data, if you continue using it. Arguably, for a sub $30 item, its not worth the time and shipping cost to claim on the warranty, either. The manufacturer is counting on most owners deciding this.
- as a corollory to 3), 2 1 Gb cards are better than 1 2 Gb card.
4) Always reformat a flash card in the camera, not on a PC. Reformat all at once rather than erase individual files.