Solid state drives have dropped slowly but steadily over the past nine months, and can be expected to continue to decline, though the December 10th 2010 0.07 second power outage at a Toshiba flash memory factory is likely to cause a short-term upward blip in flash memory prices.
The major cost of a solid state drive is the flash memory. As new flash memory capacity comes online in 2011, we can expect price declines, possibly sudden ones, which might make the 400GB and 480GB models more acceptable to computer budgets.
For most users, a solid state drive is second only to memory in improving system performance, and sometimes it helps even more than memory. And once there is enough memory, adding more does not help, but a quality SSD will always help over a hard drive, but not all SSDs are created equal.
I won’t even consider a Mac without a solid state drive any more. All my Macs have them now, and when I sometimes reboot (for testing) with a hard drive, it feels like molasses. I use the OWC Mercury Pro RE 200GB model (five of them) in two Mac Pros, as well as a 240GB Mercury Pro in my MacBook Pro.