Uhh, it's a word, right? Anyway.
2-piece set bonus
According to my log parser, Riptide accounts for 23% of my in-combat casts. This makes sense because my normal rotation is something like RT-LHW-LHW-CH, and with the Glyph I try to keep Riptide rolling on 3 separate targets if the fight mechanics allow it. The Shaman T10 2 piece set bonus grants 20% haste on your next spell cast immediately after a riptide. At level 80 1% of haste is 32.79 haste rating so 20% haste is about 655.8 haste rating.
Unfortunately, as I'm already sitting on 995 passive haste rating, that haste boost would actually push me over the GCD/LHW haste cap of 1639.5. It's not a total waste, but in my normal rotation it would lower the value of this set bonus to 644.5, and this value will get worse and worse as my gear gets better. So I'll stick with the value of 655.8, and assume that I'm going to be switching to something like RT-HW-LHW-CH. Assuming I can keep a pretty steady rotation of this, the rough theorycraft would be that this haste bonus affects a quarter of my spells, but loses a little utility because it's not really controllable, and due to the riptide cooldown, I may not have the haste proc up during a burst when I really need it.
For the purpose of future loot rankings, I'm going to say the T10 2 piece set bonus is worth about the equivalent of 100 haste to me, which probably stacks up to about 150 HEP.
4-piece set bonus
The Shaman T10 4 piece set bonus, as it is basically an uncontrollable hot, which we already have one of, and looking at the 251 T10 items there are much better upgrades from other sources for a few of the slots. I can't really think of an effective way to model it, but I am hoping it is something stassart will model and get HEP calculations on. I suspect it will account for a lot of overhealing.
Until then, I'm pretty much going to ignore it for the purpose of loot ranking, as 2 of the 251 t10 items are downgrades for me right now. I'll probably revisit it when the next iLvl of T10 items become available, or when some number crunchers on EJ find out that it's actually awesome or something.
Anyway, I'm up to I think 35 Emblems of Frost on my shaman now, so I'm probably going to revisit my planned pull list with some updated HEP stats based on these calculations, and the availability of other gear. Stay tuned!