realskiers

Agreed.  In my experience, some of the demo bindings are of very good quality.  I bought a pair of Fischer skis with a very good Fischer XTR Pro 13 demo binding.  The only reason I swapped them for a regular binding was that with the binding mounted on the ski's race plate, the stand height was too high. 

Which leads me to some general comments:

-- watch out for stand height; if the demo bindings raise the stand height, this may be a good thing if you want more edge-to-edge quickness, say on a wider ski, or a bad thing if there is already a plate on a narrow ski.  The Fischer binding mentioned above, had a 10mm higher stand height than a standard binding, and made the total stand height (ski/plate/binding) at 63mm -- that's quite a bit, and for a 70mm wide ski it was way too high and made the skis really twitchy; swapping them for the standard binding calmed things down.

-- on some demo skis, the bindings are the same as retail; eg. Dynastar/Look/Rossi Fluid system is a type of sliding rail system (toe and heel piece slide individually on a rail), and every Dynastar or Rossi demo/rental that I have ever had has had this system -- and it is exactly the same as a ski on the store wall.  Nordica may be likewise -- I recently bought a pair of demo Mach 3's in great shape that have very good adjustable bindings, and I don't plan to replace them.

-- having fore-aft adjustability is a good thing, and may be worth keeping the demo binding just for that reason, unless the other afore-mentioned drawbacks lead you to replace it.

-- if the ski would benefit from a fixed-mount bindings (flat or lifter-mounted; no plate) for flex pattern reasons, then the demo binding rail may make the ski stiffer, and definitely heavier.

Bottom line: if you really like a demo ski and want to buy it to save some money, you will have to evaluate the quality of the binding and whether it will help or hinder your skiing.  If the latter, then the money spent on a new binding won't make the ski such a great deal in the end.

Hope this helps...