Thanks for the replies guys. I actually wanted to buy a NAS solution until I read about this Windows Home Server. The NAS I was probably going to buy was the Synology CS 407, but the ones you guys recommend are very good options also, I know.

There are three reasons I prefer WHS over a regular NAS. One, WHS is -obviously- a real server, with much more CPU power behind it to back it up than a NAS. This means the Gigabit network would be a lot faster, almost up to the level of the speed limitation of the used harddisks itself, while most NAS'es stop at 30 MB/s. (That Thecus 5200 NAS seems to do better in that respect, especially the Pro version, because it uses a Celeron CPU instead of some network CPU. On the other hand the review says its noisy, making it unusable for my needs).
The second reason is multimedia. WHS is specifically designed to support and stream all kinds of media, while most NAS'es are only file servers. (the aforementioned Synology and Qnap are exceptions to this).
The third reason is cost. Building a small server with a reasonably powerful yet economical CPU and WHS is still a lot cheaper than buying one of the better NAS'es (like that Thecus N5200 Pro) and use that instead. Ok, so a real server would probaly consume a bit more power than a NAS, but there's always hibernation. (and maybe even wake-on-lan)

I know there has been mention that WHS won't be available as a separate software purchase, but I doubt this. I've even seen it pop up already in a few price lists of online shops, at about 130 euro for the OEM version.