How should a glass material be setup in Cycles? A glass-shader produces a render like this:


Adding a transparent shader creates  





Where does the border labeled as 1 come from? Why is the outer region (2) more translucent than transparent?
Not sure this is a material or lighting issue.

.blend

With out a subsurf modifier it looks terrible:



I tried several values from the IOR range 'Glass': 1.440 - 1.900

Only the upper edges and bottom are beveled.
There are a couple things going on here:


The glass is not entirely white, so a noticeable amount of light is being absorbed. Setting it to white (or almost white) gives a more glassy result:



With a less uniform lighting/environment the glass is more visible:


In this render I adjusted the model to get rid of the subsurf artifacts and thicken the bottom a bit.
There is an air gap between the liquid and the glass. This isn't the way liquid normally sits in a glass in real life, so it might look funny. See Liquid / glass interface IOR and normals in Cycles.

If the interface between the liquid, air, ice, and glass are setup as described, you get a result like this: