What's the advantage & benefits of having RAID?
The biggest advantage, excluding RAID 0, is redundancy. With most any other RAID configuration, should you lose a drive, your data remains intact and all that is required is replacing the defunct drive and rebuilding the RAID.
While you never asked about disadvantages, I thought I might touch on a couple. The biggest is RAID 0 for the obvious reason that it has no redundancy. If one drive in the array crashes all data is pretty much unretrievable without shipping the remaining drives to someone who will charge an arm and a leg for retrieval. Also, with one disk of a 3 disk array gone, you lose 1/3 of your data no matter what. If you're dumb enough to install your OS on a RAID 0 you can also forget booting your system. The other main disadvantage is cost. For a RAID 1 you need 2 identical disks, doubling the cost. For a RAID 5, you require a minimum of 3, tripling the cost. Over and above the cost of a single drive system.
How complex is the setup?
That depends on the controller itself mainly. I have a strong preference for Adaptec RAID controllers myself and find them quite easy to setup. Generally speaking, the setup is done through the controller's onboard BIOS. During POST you usually get a message like "Press Ctrl-S to enter RAID setup" and do so. For a reasonably experienced user, setup is normally fairly easy. You tell it what type of RAID you want and which disks to add to the RAID. Then the disks (RAID) must synchronize and it's ready for use. In my experience with RAID's because of the synchronization, it's always best to do this before installing an OS as the more data you have, the longer sync'ing takes.
I've yet to buy a motherboard with a built in RAID controller so can't even begin to compare them to controller cards. Someone else mentioned that frequently onboard RAID controllers aren't capable of RAID 5 without an add-on card. I wasn't aware of that for the above reason. I assume that isn't necessarily always the case though depending on motherboard and onboard controller.
Would you recommend that anyone do it?
Not really. For the average computer user a single drive will work just as well as a RAID. RAID has mainly been intended for servers or other high end machines where redundancy is required. On the average home PC, a reliable, regular backup should suffice.
I have noticed a lot of people (ok, as ham30 mentioned....mostly gamers) are using RAID 0's these days in an attempt to "speed up" their systems. Any possible performance gains are at computing speeds which wouldn't really be noticable to the human eye during 'game play'. Most of those are likely software RAIDS configured within windows itself. If you're interested, a search on MS's site should yield information on configuring software RAIDS in Windows.
To be honest, I think in a lot of cases having a RAID 0 on a home PC has become a case of bragging rights.
A good *HARDWARE* question might be: Which are the most manageable, reliable RAID CONTROLLERS?
A very good question! As I stated earlier, I have a strong preference for Adaptec. I've worked with LSI controllers and a few others I don't even remember the name of anymore and was never as impressed with any other as I have been with Adaptec. Of course like all opinions, that's just mine and I'm sure there are a lot of different ones out there.
Myself, should I ever decide to build a RAID system at home (and the only reason I would do so is if it were a server) I would likely go with Adaptec. However, I would do some google searching and comparing regarding cost and capabilities before making a final decision on what to purchase.
The problem is that this still didn't protect against a failed OS or virus because that would affect both drives as the second one is always an exact copy of the first. But this is true for every Raid option!
No RAID configuration that I know of can protect you from a virus or failed OS. If you know of one, please tell me what level of RAID that is as I'm sure the place I work would be interested in knowing this....as well as every other IT department in the world....
The point of RAID is not to protect you from virus's (that's what antivirus software is for) or failed OS's (that's what backups are for)....it's to protect your important, and often unreplacable, data....which RAID's do quite well (again, excluding RAID 0)
I would go with the RAID 5 configuration. Or possibly a RAID 10 since you have 4 drives. That's a combination RAID 1 + RAID 0 configuration.