Considering current alternatives to HDD, such as the "old", Silicon Disk type:
http://www.globalspec.com/FeaturedProducts/Detail/ContecMicroelectronicsUSA/Silicon_Disk_Drives_V_Series/13056/0
to it's "new" rival types such as:
http://www.adtron.com/products/
and with the rapid drop in flash memory price, it is fair to assume the solid-state take-over, of traditional HDD role in PC (for scratch-padding and adaptable segment storage) in computers.
Maybe not yet so for permanent documents storage, after all, HDD is a proven and reliable technology, but still prone to some weird occurrences, one being described recently in:
http://cr4.globalspec.com/thread/5941#comment43908
If PDA and Cellular Phone technology are pointers to future PC-Application to any extent, it should be so because of it's outstanding performance in a relatively poor resource-base, meaning it's processing power and memory capacity. Many of those having ROM based OS of firmware, and flash memory for random access of data.
This is I think, a valuable lesson both Desktop and Laptop development, and some of the traits in these smart little gadgets take-on the big boys hands-down.
This mention was mainly in contrast to the lavish resource spread of means in PC versus such a (relatively) poor yield in efficiency, that is, when generally compared to PDA and Cellular.
Of course, when compared in absolute terms Desktop and to some extent Laptop are the best available to the private sector to-date, but this post is about mentality of design:
We all need predictable, reliable, fast, soft driven machines. The question is how to achieve it, with the best resource to yield ratio, because we collectively are a six-billion-resident global village, and the ecological clock is ticking faster than ever.
Yes, the type of memory used, may boil down to ecology.