CD-ROMs are slow. Direct cable connections are hard to set up. USB flash drives, though, are speedy, rewritable and nearly instantly recognizable between all sorts of devices. And now that they're ubiquitous, they are also becoming irrelevant.
Flash drives deliver enormous convenience. They store many megabytes or gigabytes of data for a few minutes or for many months. File transfer speeds are fast. These capabilities come in a chunk of plastic small enough to dangle from your keychain.
There's just one problem. Now you can access numerous free cloud-storage services such as DropBox. Instead of dealing with a physical (and easily lost) object like a USB drive, you can just snag your files from the web anywhere you have Internet access.
Flash drives were a wonderful thing. Their short stay atop the technological mountain flashed by far too fast.