Just spent so time and money upgrading my MacBook and iMac Systems. Added 16 GB of Core to the iMac, (32Gb Max) and added 4TB of rotating Memory via Firewire. Put a 750GB/SSD Hybrid in the MacBook, and bumped the core to 6GB. (Max for that model) It took a while to figure out how to move the BootCamp (windows) Partition to the new drive, so that it would be Bootable. Once that was fixed, things sure work a lot better, with that SSD Cache working. I also made a backup, of ALL my Rotating Archives onto a backup HDD, to be stored Off-Site. Added another 2TB HDD to the Drobo. So it now has 5TB... Adding another 1TB HDD, to Momma's iMac via Firewire, and Maxed Out her Core Memory to 3GB. Should be good for another year, at least.... Well maybe....
That the Seagate Momentus XT 750? I have the 500 (4GB NAND Flash while the 750 has 8GB) and have had great results although it didn't seem to work so well in Macs. The 750 is supposed to be much better. It constantly analyzes and places your most used files into flash for SSD like responsiveness and the 750 is SATA 3 for 6Gbps... It gets better over time and you'll find that even after 5 or 6 reboots, nearly all of your system files will be in the Flash section. At $179, I think it's the best 750 GB drive on the market and I'm planning to pick one up as a secondary spinner to go along with an Intel 520 SDD (OS)
If you're going to run a lot of disks on your Mac, you might like running ZFS. This was ported to the Mac from big Sun/Oracle enterprise servers, and is made for redundancy/resiliency, taking snapshots, and extending the capacity of a volume by adding disks to it. Ten's Complement LLC | ZEVO | Storage
Actually ZFS is more like LVM + RAID + compression + de-duplication + remote replicas (backups) and probably more. LVM is just a subset of what ZFS can do.
I'll just stick with my Drobo's.... Got another one coming this week.... good enough for the bush.... and Yes, that was the 750 Momentus XT... really liking it.....