I moved a small 4TB database from 24x 256G 15k SAS drives to 24x 240G OCZ Vertex 3 SATA3 drives. I ran a few queries on the old and the new. same data, same parameters, same amount of data pulled. Both were hooked up via PCIe 8x slots.
the SSD crushed the SAS. Not just a mere 2x or 3x crushing. A _FIFTEEN TIMES FASTER_ crushing. This was pulling about a million rows out. 12 seconds (SSD) vs 189 seconds (spindles)
Cost difference? under $50 per drive more expensive for SSD. I think our actual rate was around $10 per drive more. However, the system as a whole (array+drives+computer) was $12k less. No contest... for our particular application, SSD hands down makes it actually work.
we'll be moving the larger database (same data, same function) to SSD as soon as we can.