It's not just aspects like performance and data security that should be considered; in many cases, enormous amounts of data must be managed and stored - the right approach to tackling this problem is a RAID array with large hard drives. Because expensive SCSI RAID adapters and SCSI hard drives were the only available options just a few years ago, high-capacity arrays were feasible only for very few individual users or companies.
Today, the prices for IDE hard drives with a capacity of 100 GB have dropped to a few hundred dollars - a downright bargain. It takes only $500 to set up arrays with a capacity of 300 to 400 gigabytes. The introduction of new hard drives with up to 200 GB will make RAID arrays with up to 1 teraByte (5x 200 GB) affordable for the first time ever.
Muddle Makes Trouble
No matter which RAID array you're using - for the operating system, it's ultimately a drive just like any other, and therefore it needs to be maintained accordingly.
You should defragment it at least a few times a year; for more heavily frequented drives, once a month. Ideally, you'll enter the defragmentation program in your task planner and have this pesky operation performed during acceptable times.
If one of your drives ever begins to snarl (louder operating noise, reduced performance or other conspicuities), don't hesitate. You should back up all of your important data, especially if you're using RAID 0. If the operating system is on the RAID array as well, you might want to try and mirror the drive in question on another computer with an identical hard drive. Otherwise, you'll have no choice but to reinstall everything.