$99 for a box that can very effectively stream video from your NAS? Sounds like a winner to me.
I run Plex (a Mac-only XMPC derivative) on a Mac Mini, but $699 is a lot more than $99. If your storage is NAS already, about the only advantage the Mac Mini has over a jailbroken AppleTV2 is the ability to play Hulu through Safari and not get blocked. (Well, it's also a lot faster and mostly future-proof as new codecs are introduced.)