Write Endurance
Still not keen on the idea of using MLC flash for enterprise-grade storage...
Even the best 2-bit MLC flash has a relatively short lifespan compared to most single-level cell devices (note that this assertion does not take into account wear-levelling and the use of TRIM commands to extend life).
STT-MRAM (Spin Torque Transfer Magnetoresistive Random Access Memory) shows quite a bit of promise
-- -- http://en.wikipedia.org/wiki/Spin_Torque_Transfer
-- -- http://en.wikipedia.org/wiki/MRAM
but is some years away from production, and with fab construction (or conversion) costing billions of dollars, you can bet that flash manufacturers are going to milk the technology for everything they can get before they're forced to switch to a different technology by nano-scale quantum effects.