Didn't Kelloggs develop cereal drives? I think they were a bit flaky, though.

I can think of some applications for Write Only Media...!! Nuff said!

Unfortunately, my experience is that flash media isn't to be trusted for anything other than carrying data from one machine to another - they can fail without warning and there's no way to recover your stuff... and it doesn't seem to matter how cheap or expensive they are.
Even if the manufacturer offers a warranty, what help is that when your data is lost forever?

No storage medium is 100% reliable, but data from failed hard drives can usually be rescued, although the service can be expensive.

It's also worth remembering that most pen drives and memory cards use FAT32, which limits the size of individual files to 4Gb irrespective of the drive capacity.

I carry two cards around with my camera, but I also have a portable card reader with internal 80Gb hard drive, so that I can back up my photgraphs soon after I've taken them without needing access to a computer - and it's far more convenient than a laptop.