NAND flash chips, not unlike those used in SSDs, will be part of the norm
This may be more of a repeat, since predictions of this sort have been done before, but Toshiba is one of the three premier HDD providers, so when it talks about such things, people listen.Indeed, Toshiba made a statement the other day, one that has to do with hard disk drive, both traditional and more revolutionary ones.
Long story short, the company believes 50% of all HDDs will be hybrid units, with integrated NAND Flash chips, by 2015.
The NAND Flash part essentially turns the HDD into a part-SSD device. With the OS and other frequently used files stored there, the whole system is guaranteed to work faster. Application boot time, for example, is reduced by 40%.
Full SSDs will gain some ground over the next two years as well, but not enough to drive HDDs out.