At home I've been storing all my data on my Media Center PC. That machine had 3 x 500GB SATA drives set up using the on-board motherboard RAID 5 controller. The setup has served me well for the last year but I had been watching the progress of Microsoft's Windows Home Server product and once I saw the quite beautiful looking HP MediaSmart Server I decided it was time to have a dedicated NAS solution.
The HP EX470 is well designed. It is small, headless (no monitor or keyboard/mouse ports etc.), fairly quiet (even with four drives in it), and looks sleek. The drives use hot-swappable pull-out trays and colored lights give you at a glance status of each drive, network and overall health. Internally, the EX470 has 512MB of ram and an AMD Sempron 3400+ processor. The processor appears quite capable but I strongly believe HP should have put at least 1GB of RAM in the machine. My first job was to take the device apart and replace the stock ram with a single 2GB stick which definitely provided performance improvements (especially noticeable if you remote desktop into the machine).
I then added my existing three 500GB drives to it (a very simple and quick process of putting the drives in the trays, inserting them and using the graphical user interface to format them and add them to the storage pool). I also installed SlimServer software which powers my network audio players. While the SlimServer software is not officially designed to work with Windows Home Server it works fine 
Windows Home Server is actually a stripped down version of Windows 2003 Small Business Server (yes, you can find places where it says that if you poke around) with the Home Software on top. Instead of using hardware RAID, WHS provides a flexible mirroring solution where it ensures that for shares you enable mirroring for that there is always a duplicate copy of each file stored on another physical drive (obviously this is only available if you have more than one drive in your system). As you might expect, when you add drives you get more available storage space and the rest of the devices on the network simply see one logical device.
This approach does have some pro's and con's. The pro's are that the physical drives use NTFS so in a worst case disaster you can pull out a drive and read it on any Windows machine, you can add, remove and upgrade drives of different sizes (in hardware raid all drives need to be the same size) and you can choose which shares are mirrored/duplicated instead of an all-or-nothing approach.
However, there are some drawbacks. The mirror/duplicate files are created by a background service thread, this means there could be some time between the creation or update of a file and how quickly the mirror copy is made and there are some performance bottlenecks to be aware of. When a new file is stored on the server it is first written to the primary drive and then migrated off to one or two secondary drives (depending on if mirroring is enabled) by the background service. When dumping a large number of files you can guess what happens, you see a lot of disk contention on the primary drive as you have concurrent write operations competing with the background service reading the data and migrating it to secondary drives.
My plan is to also run the SageTV Server on the box for video and television media and possibly to use it as the master server for my CQC home automation software.