I had some bad performance problems with my new NAS box running ZFS which resulted terrible video and audio lagging problems in windows when I tried to stream video from zfs share via CIFS to a media player running in windows. Even playing mp3 music files from CIFS share in Winamp resulted with very bad lagging, like I was playing a very scratched CD.

I asked help from opensolaris forums (very friendly people there!) and ended up bying a new Intel Gigabit Ethernet PCI card for 25 € which replased the Gigabyte motherboard onboard Realtek 8111B network chip and fixed my problems.