I'm mostly concerned about the power cord getting unplugged if, say, somebody is vacuuming around the area. On top of the usual "whole machine gets turned off" failure mode that happens maybe 10-20x a year in my neighborhood because of power loss there is a "machine is turned on but HDD is powered off" case.
Personally I don't trust a NAS as far as I can throw it, or rather I'd use one the way I use Amazon S3.
My home server has a ZFS array, the media server and some other programs access it directly. If I want to move files to or from it I use SFTP. If I want to back files up to it I use rsync. I have Lightroom running pretty good on an external HDD, no way I'd take my chances running it on a NAS.
An appliance with the primary role of storage, and the ability to share files over the network are the distinguishing features for a NAS. Network support for iSCSI, SMB, NFS makes a NAS; sharing data exclusively over the media protocols (http, rtsp, etc) makes it a media server
By "NAS" most people mean "box they bought from someone to share files on a network" - think Qnap or Synology. They'll call a "NAS" that is home-built a server, even if they do basically the same thing.
To make it more fun, you'll have people refer to "I don't have a NAS, I run FreeNAS on my server."
