Those who transfer a significant amount of data via the NIC.
Personally it means nothing to me... I peak at maybe 8MB/s on my home LAN, and my 2500mbps internet connection obviously isnt going to use up much bandwidth at all.
Just over 8MB extra traffic on the PCI bus isnt nearly enough for me to give a damn about CSA.
Now were I to use Gigabit LAN to it's maximum abilities.... that's 125MB/s downstream and upstream, 250MB/s total which is by itself well over the peak of 32bit/33MHz PCI bus. Definitely wouldnt leave much bandwidth for other devices.
If all your using the NIC for is your internet connection, or a basic home LAN without huge bandwidth needs then CSA probably isnt going to yield you much benefit.