I've used lots of options, including WHS, unraid, regular RAID, windows/linux/freebsd dedicated servers, etc. I now take a simple, ghetto approach. I have a bunch of hard drives in my office PC with them shared. No RAID or redundancy, aside from manually mirroring anything that I can where ever it will fit. It's simple and works. If I ever have a drive failure, I'll restore anything that's quick to restore and the movies I watch most (which are a small subset of my total collection). The rest would most likely be movies that I never watch anymore anyway so I wouldn't really care.
Keep it simple. That could be as simple as hooking up a large external hard drive directly to your HTPC and hiding it directly behind it. If you really want a dedicated NAS or server, just put it anywhere that's out of sight and connect it to your network. That's what networks are for.