a potential to use a lot of flash as it continues to drop in price
The CD is already obsolete, and while it can be argued that the sale of music and movies is gravitating to the virtual world, we have a few years to go before downloading of entertainment becomes accessible and pervasive enough to eliminate the need for a physical system of transferring this type of data. Also, don't forget that physical systems still can deliver a bit higher level of intellectual property protection than data.
Look at how difficult it is to transfer music from one ipod to another, or to load music from one home computer to another. Yes Apple has great hardware, but really the software is clunky and irritating. Not becuase Apple can't write quality software, but rather, because it is built around the idea of IP protection instead of being totally devoted to the consumer experience.
Result, phisical conveyance of data will stay around a lot longer than it should. And, a great deal of buying is impulsive. So, as long as people visit physical locations, they will buy physical music.
As traditional music stores continue to disappear, other retailer will seek ways to continue to serve the physical niche and have a desire to use less square footage to make physical selection of music available at grocery stores, convenience stores, starbucks, etc. They key evolution will be packaging and a way of conveniently organizing a few dozen of these cards into some type of wallet.
Maybe this won't be the hit the Sandisk hopes it will be but it does have it's place in the market and a certain type of utility.