It's strange that you guys are seeing performance issues.
My DNS-323 is connected to a 10/100 router and my Windows 7 laptop is Wireless N 300Mbps.
I've just transferred a 2.5GB file to the DNS-323 and Windows reports a speed of ~6.28-7.24MB/second without modifying anything.
The same test connected via an ethernet cable to the router shows ~10MB/second