It took Linksys a long time to finally retire its EFG120 and EFG250 NASes with products that can compete with the current crop of RAID NASes. But it appears that the wait was worth it. The NSS4000 is a business-oriented RAID NAS with features such as its optional redundant power supply, virtualization, VLAN support and dual gigabit Ethernet LAN ports that set it apart from the increasingly crowded pack.
The one standard feature I would have liked to have seen is the ability to do a ssh login to a command-line interface. If I'm a business trusting my valuable data to this device, I'd be much more comfortable if I had the capability to bypass the web interface if anything went wrong. But maybe that's just me.
The other thing that might give buyers heartburn is the hard limits on number of simultaneous users. The numbers are set reasonably high (15 CIFS / 20 NFS) such that small offices might never encounter a problem. But in larger shops, this could provide some agita for system admins.
But otherwise, the NSS4000 is about as full-featured as you can get for a business-class NAS and should be a big seller for Linksys.