I found this tweak that alters the acknowledge rate of your TCP packets to acknowledge on every packet from the server instead of every 2nd packet. This has reduced my latency in game from around 180-220 mark to 70-90 mark.
Not specifically Shaman related I know but its done wonders for me and I thought I'd spread the word. There is a full undo script if you don't get a benefit from the change (unlikely). I've also analysed what the script is doing as I'm that paranoid and can give it my personal seal of approval and recommendation. This is a completely genuine script that simply tweaks a windows default to make your game run with less lag. It can an will improve your dps by reducing your lag.
NB. You won't notice the difference in Lagaran, nothing can make that place lag free other than Cataclysm.