SSD in the Enterprise are usually SLC and not MLC devices. Big difference, and hence the big price difference as well, where a 200GB SSD for an EMC or HDS array will be list for like $20k.
Yes, some applications may warrant a full on SSD array, but when companies offer block level tiering now (EMC Fast v2, HDS HDT, 3PAR, Netapp) the overall amount of disk spindles goes down while space goes up. Your grouping SSD, FC, and SATA disks into one large pool where the array controller if able to detect and move blocks of data between the tiers. Better performance, more disk space, less physical space, cheaper cost.
