As an IT guy, I see stuff here that is right and well thought out and stuff that's wrong. Most of that has been sorted out by now so I'll try to comment appropriately...
OS Setup - I could get into partition alignments for SSDs, etc but suffice to say SSD is the only way to go for the OS and apps. Turn off the pagefile because all it does is wear out the SSD and isn't necessary. Ditto big time for Defrag. DO NOT USE DEFRAG with an SSD! Windows Vista, 7 and 8 are SSD aware if you install from scratch and will automatically align themselves during install if you set up the partition and format during install. They will also disable the Pagefile and Defrag automatically if installed on the SSD. Try to make sure the BIOS is set for AHCI or RAID in order to get the most benefit with data transfers. SATA III is also best for the SSD drive. Some systems only have one bank of SATA III.
SSD - Fastest solution available, getting more affordable but read up on latest tech because it has also changed a lot in the last year. Hard to go wrong with the latest Intel, Samsung, Sandisk, OCZ Vertex or Crucial M series. Corsair isn't bad either but I haven't kept up with them lately. If you want to be lazy, buy from NewEgg and read the reviews first.
Where it put OS? SSD. Where to put Lightroom/Photoshop? SSD. Where to put catalog? SSD. Where to put photos? SSD but likely you will run out of space so this depends on convenience vs performance. In general, you won't lose a ton of performance if you put the photos on the spinning platter drives. This way you don't have to spend a lot of time moving pictures around in the catalog when you move them from the SSD to the larger volume for space reasons.
RAM - you can't have enough. I use SSDs and I still noticed a huge increase in Lightroom 4 performance when I went from 16G RAM to 32G RAM. Lightroom 4 is a dog. i7 system with SSD, RAID and 32G of RAM and it still runs 30 to 50 percent slower than LR 3.x. Grrr.
RAID and BACKUP - You can sink a lot of money into the computer fast. These digital pictures we take with abandon require a lot of storage space. Since they are important, they require redundancy and backup. I have a 120G AHCI SSD for the OS/Apps and three 2TB RAID 1 (mirror) volumes. A RAID is NOT a backup. It is drive redundant fault tolerance. You still need Backup and preferably a rotating external backup plan so you can keep one drive at a time offsite. I have an internal 2TB drive for backup and then I use 5 external 2TB USB3 drives for backup and rotate them weekly. And that's still not big enough for everything, it just covers the past year or two's data, (one 2TB current work volume). The rest is archive and doesn't change much.
I could go on but at least make sure you are doing multiple backups even if it's only to an internal hard drive. I do MWF, TTS, Sun Weekly and Sun Monthly to the internal and external then I rotate external drives once a week. This gives me plenty of backups to go back to if necc and the internal drive is used so if an external fails or gets disconnected, the backup still happens.
