As documented in the excellent Enterprise Flash Drive Cost and Technology Projections overview here on Wikibon, the two most popular justifications for deploying Solid State Storage solutions are (1) to reduce operational "green" costs, and (2) to improve I/O response times.
However, both of these justification scenarios de-emphasize overall capacity, while the first also assumes short-stroking limitations cannot be overcome with multi-tenancy wide-striped LUN's using thin provisioning technology.
The advent of primary storage deduplication now offers an enticing third justification scenario which builds nicely on the first two, without sacrificing capacity. Imagine a "mirror asymptote" overlaid on top of this diagram but descending from the opposite side. That asymptote would use the same scale but reflect the dedupe ratios of popular enterprise data sets. For example, 10:1 is common for virtual desktops, 5:1 for virtual servers, 3:1 for scientific data and data warehouses and so on.
Therefore the intersection point between the asymptotes represents where deduped flash becomes lower cost than the equivalent capacity of primary disk that is not deduped.
Action Item: Now more than ever, it's time to examine your primary Tier 1 data sets for "de-dupability". The cost-neutral opportunity to transparently reduce the OpEx of your most expensive tier of storage while simultaneously improving I/O response times by an order of magnitude is manna from infrastructure heaven.
Footnotes: Enterprise Flash Drive Cost and Technology Projections | Diagram of Flash Premium to Disk