Where the front of the dark heel wedges in the shoes end, the light, firmer, tan midsole begins. It is at this point that you can feel a distinct rocking effect. The Skechers have almost none of this because their wedge is much longer towards the front of the shoe.

The other thing about these shoes is that they have a tough flexible plastic "energy wedge" [my term] that is embedded in the heel. These are supposed to absorb the heel-strike energy and then help the heel rebound by returning the energy as the heels lift off.

Avia calls this it's "Shear Cantilever System" and it may allow these shoes' heels to last longer than the Skechers because all the Skechers have is the outsole and then the pillow soft "Kinetic Wedge". It's my impression that the softer Kinetic Wedge in the heel will break down faster than the tough-looking Avia Shear Cantilever system but this is just an impression.

The Skecher is very comfortable from the outset while the Avia is more ridged feeling (more stable actually) so the Avia rocking motion is very "directed" forward while the Skecher is less fussy about which direction you move (including side-to-side).

The other thing about the Shape-Ups XT is that the width of the outsole, moving forward towards the front of the shoe, is about 1/4" narrower than the Avia. And the tread is more aggressive, and is broken by areas that allow the foot to flex a bit more as it travels forward (Avia calls these "Forefoot flex grooves" that allow for natural Dorsi flexion".

Also:

(1) this shoe is distinctly lighter in weight than the Skechers.

(2) it does not have a nylon loop lacing system like the Skechers; using the traditional lacing holes instead. I have read one Skecher review, and I have experienced it directly when trying on a pair Skechers, where one of the nylon lace-holding loops came loose from the shoe. So I can only conclude that the Avia's are longer-lasting in this area.

Avia's wider heel and deeper tread will probably translate to a more stable footing for trail hiking for people who are unsure that a Skecher could handle a trail or two.

Update 8/9/10: I now own these Avia shoes AND now Skechers Shape-Ups XTs.

The differences now that I have them both is that the pressure hits you differently when you place your foot down. The Skechers feel like there is more pressure on the heel whereas the Avia's almost immediately feels support spread over more of my arch. The Skechers also feel less stable when I stand on them (they are in fact known as "unstable rocker sole" shoes like the MBTs), whereas the Avia's feel more stable; even though they have a raised pivot point in the middle of the sole that actually causes a little instability when you place them on flat surface. I.e. the shoes don't sit flat on the floor and even slightly wobble laterally left to right. In practice, I don't notice this lateral wobbling much when I am wearing them.

When simply standing, the Avia support feels more centered (bunched) under the arch whereas the Skechers feels like the support starts more towards the heel and extends forward towards the middle of the arch. This feeling is not right or wrong, just different.

So far, I would certainly prefer the Avia's on a trail than the Skechers.