Spinning disks are hanging on to the very large end of the curve, where cost per GB really bites, but "smaller" drives (under 1 TB) are rapidly switching to SSD storage. I wouldn't count on that holding much longer, though. If it were straight replacement for incremental improvement the march would be slower, but the fact is that SSD storage has clear and significant improvements. This is true even when it uses SATA interfaces, which are clearly not optimized for SSD. Wait until PCI interfaces become mainstream.