You might want to read this:
http://forums.dlink.com/index.php?topic=3689.0
I just upgraded from a 100mbps network to a gigabit network. I spend some $$ on gigabit nics and switches. My performance gain was almost laughable. Was it faster than my 100mbps network? Yes, but slightly.
I was able to get about 8MB/s on my 100 mbps network. When I upgraded to the gigabit network it went up to 12Mb/sec. It's a 50% improvement, but I was expecting 3x-4x (300%-400%) improvement (23-32Mb/sec). I then tried a simple copy of an iso from one machine to another and I was able to achieve that 300-400% improvement, but the limiting factor is the NAS. It supports a gigabit interface, but you won't be able to do much more than slightly better than 100mbps network (due to the HP of that little NAS).
If you want a fast NAS, you're better off with a NASready PRO, but they are expensive. For the price, I'm satisfied. I only paid about $80 for my dns-321 on black friday.
Gary