The DNS-323 might be thought of as D-Link's somewhat belated response to Netgear's SC101. Both are two-drive RAID 1-capable BYOD NASes with easily installable drives and similar physical sizes. But fortunately for D-Link, that's where the similarities stop. The DNS-323 uses SATA drives instead of the IDE drives used by the SC101 and a gigabit Ethernet port vs. the SC101's 10/100. The 323 also sports print, FTP, UPnP AV and iTunes servers, where the SC101 has no built-in servers. Finally, since the DNS-323 supports the standard SMB/CIFS network filesystem protocol, it can be used by machines running OSes other than Windows including Mac OS and Linux.
A fairer comparison would be to Thecus' N2100 Yes box, which accepts two SATA drives and supports JBOD, RAID 0 and RAID 1. The N2100 also has an iTunes and FTP serving, but has a "community photo webserver" instead of a general-purpose UPnP AV server. But since the N2100 is $50 to $70 more expensive with an inferior feature set and comes from a lesser-known company, the 323 is more likely to end up in buyers' shopping carts.
The biggest competition for the 323 could be from HP's Media Vault, since it comes from a "name" vendor, has a similar feature set (sans the iTunes server, alas) and better performance than the 323 in some modes. The Media Vault's pricing is competitive, too, at $349 for the mv2010 model that includes a 300 GB drive.
D-Link just needs to get the DNS-323 into stores in time to hit the end-of-year buying season and pump out new firmware that addresses the bugs that I found and hopefully adds new features. If D-Link can get the job done, then they could really have a hit with the DNS-323.