The article that Steve links to is very interesting (Thanks, Steve).

I think that flash hard drives offer a solution to a problem that's been dogging desktop and laptop computers for a long time - boot up speed. Some have suggested that the time spent in boot up could be greatly reduced if we could come up with a better way to make the operating system available. Early suggestions have include putting simple versions of the OS in ROM. Most users want to boot up and immediately do something like check email. Using this paradigm the user gets a quick boot up and checks email while the rest of the OS is loaded into memory in the traditional way.

ROM sounds good at first, but it's hampered by the need to occasionally update the OS. Can you imagine the losses that would be incurred if a major manufacturer released a machine with OS in ROM and someone discovered a security or virus vulnerability? You'd have to replace hardware all over the place. Answer: keep a simplified version of the OS separated off in flash. Updates can be sent out whenever needed. This takes advantage of the fast read times of flash while minimizing the downside - degradation by too much writing.