Funnily enough this is something I was thinking about myself... I heard about "Stablebit Drivepool" which I believe is only for WHS, but I like the idea. As far as I can understand it's like a weird type of psuedo-RAID where an application monitors your folders and just ensures that certain flagged folders or files always exist on 2 physical drives at once.
It's a third-party implementation of Drive Extender, a feature the original WHS had. Drive Bender is another product that does the same thing. One of the two can be used on any version of windows, not just WHS.
Both allow you to combine hard drives into a single pool, or create multiple pools (so you could put your fastest hard drives into one pool, and your slowest into a second, backup pool, for instance.
Each pool is treated as a single drive volume, which in WHS 2011 especially is handy for getting around the 2TB volume limit. Drives in the pool do not need to be the same size, and no space is lost for mixing mismatched size drives.
You can create shares within the pool, and then set duplication on whichever shares you want: those that are duplicated will be invisibly mirrored on at least two drives. If a drive that contains duplicated files fails, you don't lose data - the files are copied to another drive, and you can put a new drive in when you want, and you suffer no downtime or degraded performance while the data is being rebalanced.
Unlike W8 Storage Spaces, this works at the file level, so you can break apart a pool without losing data. In fact you can take a drive out of the pool, and machine, put into any other machine capable of reading NTFS file systems and copy the data off it.
It's not as efficient, space wise, as RAID (or Storage Spaces in parity mode), but space is cheap these days. These two programs both provide extremely simple drive management, perfect for typical home server users.