G'day,
Thought I would "bump" this topic and pop Tiered storage for SSD/SAS/Sata Previous post
I agree with enealDC that SSD are the next evolution. The performance we are seeing with Databases on SLC in RAID1 is outstanding. But lets face it, it will be a long time before 1.5TB SATA are displaced by SSD.
But the amount of data that benefits from really high IOPS or transfer rates is actually quite small (in my experience). Most data on our clients networks is taken up by images and email(PST's).

So the ability to seamlessly shift frequently accessed data to faster storage and older/archived data to cheaper storage would be fantastic.

Cheers Ben