None of them offer an integrated data protection system. That is a system that prevents data loss from virus or simply pressing the delete key.

Also, most are hard disk based which causes them to have some number of years till the drives fail.

http://reviews.cnet.com/5208-7590-0.html?forumID=67&threadID=28919&messageID=328179 is a testament to this issue.

-> Yes I use a NAS, but I also have a backup system to add reliability.

Bob