I have skied the 88xTi now for about 10 days straight, in Utah and some local small hills. Various conditions, various runs.
I used to ski older model of the same line, before they gave out, namely Magfire 82xTi.
AFAICT, right off the bet, I will say that amphibio works on hardpack, but the extent of it being revolutionary is debatable. I do think that inside ski tends to follow better and that I can get away with loaded inside ski and some A-frame posture. It also tends to hook less and way less catch an edge. So in essence, I do think that amphibio works. Now, is it really game changer, I am not so sure of that.
What I think is a real benefit is the new version of waveflex. Ski is lighter than previous models, less swing weight, and it actually feels softer to bend, but more torsionally rigid. I have no clue how Elan pulled this off, but 88 now feels more stable and easier to ski on hardpack than my older 82xTi! If you charge hard, in deep turns, ski even feels too easy to turn, you do not feel resistance to it bending that much. Nevertheless, it never looses an edge, and it never gets deflected by crud, at least it did not for me ... very impressive I have to say.
I am about 6ft2, 220lb, and I ski it in 178. I did try the longest version, 186, but I felt it was too long for tight spaces and for bumps. Also, it was not as turny as 178 (felt more like a real GS ski), so I choose a shorter version, since I will mostly be using it on groomers and on softer, tracked out snow.
That being said, this is not a primarily powder ski, it is more of a one-quiver type ski. For me it does sink a bit in the powder (longer version would probably be better), but it does a good enough job overall that I do not have to go back to the car and switch skis, but if I know I will ski powder all day, I would choose something else. I had a chance to try out Kendo and Mantra from Volkl, and I think these skis are better in deep snow, are somewhat softer in a turn and produce better flotation in knee deep powder. On the other hand, in soft afternoon tracked out snow, I would give 88xTi and edge, it was more stout, predictable, not as easily deflected and overall had a bit more damp feel to it. On the harder snow there is no comparison, elan just blows both Kendo and Mantra away in all aspects :)
The closest ski to amphibio 88xTi that I skied was probably Kastle's mx88. I would still give elan the overall edge (heh, that is why I got them :) because they work better over a larger speed/skill envelope equally as good. mx88 was too stiff on slower speed and too demanding when pushed to the limits compared to 88xTi. I did not ski mx88 in fresh snow, so I can not compare that, but in a day old tracked snow it was about the same, in my view.
Ah, also, +1 for switching left/right skis on softer/pow days.