that flash memory was so expensive it was only viable for applications where you only needed a little bit of storage, like storing your contacts list in a cellphone. Then it got to the point where it took over as the standard storage media for digital cameras and mp3 players, remember the microdrive? it's gone now, and hard drive based mp3 players are the exception not the rule these days. Now flash is beginning to move into the consumer pc space. This was first seen in cheap netbooks with 4-16gb ssds, but increasingly they are popping up as a high end option as well. It's pretty clear that rotating media is on the way out. I don't doubt that it will maintain it's cost/gigabyte advantage but it will likely be relegated to a role as low speed, infrequently accessed storage while ssds take over as the primary drive in laptops first and then desktops. It's possible a tipping point could be reached both as the performance delta between rotating and solid state media increases and as software companies beginning writing programs to take advantage of ssds until eventually the performance of rotating media is so abysmal they are no longer used and software companied forget about them entirely.
It's important to note too that while rotating media has a cost/gigabyte advantage it cannot go below a certain price floor due to the inherent and unchanging costs involved in manufacturing a precision mechanical device. For example the cheapest you can get a new 2.5" hdd these days is about 50 bucks, however even if a manufacturer were to make, say an 8 mb hdd it probably still wouldn't be much cheaper than that just due to the costs in making a magnetic disk, precision enclosure, bearings, etc. However ssds can easily go below this price. What this means is that ssds could potentially take over the low end of the pc market by offering cheap low capacity drives that hdd manufacturers are simply incapable of matching in price.
To better illustrate this lets look at the 64 Gb ssd, which is retailing for as little $150. As a quick back of the envelope calculation let's say that the cost/gigabyte of flash memory drops by half every 18 months, and working from that number lets say the cost of our ssd drops by 40% every 18 months. In 3 years then a 64 Gb ssd will be selling for around $50, the same price as the cheapest hdd available. In 3 years of course that low end hdd could very well be 500 gigabytes. But there are plenty of users who would likely take the ssd for its performance advantage, and once the cost goes below $50 it will suddenly be the cheapest option available. Keep in mind too that a 64 Gb ssd is perfectly capable of running Windows 7 with plenty of programs installed and some usable storage left over as well. It's perfectly viable for a lot of users and would provide much better performance than any other option.