With the current high NAND price, many manufacturers are focusing on lower capacity consumer versions for boot drives and larger versions for enterprise servers.
For example, I have a 60GB SSD, which is plenty for all my OS & applications that benefit from the speed. Everything else is on my 2TB HDD with a second 2TB external HDD to periodically sync as a backup. I will not be replacing this 2TB with an SSD until the time comes when SSDs are reasonably priced as a general storage medium.
Think of both storage technologies as electricity, with HDD representing the power grid and SSD representing disposable batteries. You could run everything off the mains to eliminate the cost of buying batteries, just like how most PCs are run on HDDs alone. Batteries give the convenience of portability, while SSDs give the convenience of speed. Yes, you could run all your appliances on batteries, but just like replacing your HDDs with SSDs for bulk storage, running things like fridges, lights, etc. of large batteries would be cost prohibitive. So does that stop people using batteries? :disagree:
The best way is to combine both, for example, use HDD for bulk storage that doesn't benefit from the speed, just like using the grid power to run fridges, lighting and so on that don't need portability and use SSDs for the content that actually benefits from the speed such as as software and the OS, just like using batteries in portable items such as cameras, flash lights, etc. to get the benefit of being able to run them independent of the power grid.
On the other hand, it would be nice to see SSD pricing eventually come down low enough to actually replace HDD for bulk storage, especially in full size laptops which don't have a second HDD bay to fit both a HDD and SSD. At the moment, the main role would be to compliment HDDs like I described here in desktop PCs.