Here are a few graphical glitches I have encountered in my travels using the Mac Client.
Polychromatic polygons on the guild ship ring:
Little white puffs all over the main hall in House of Death Undone:
These puffs float off the floor and look almost like they are shining from another room behind the walls.
Bent trees in Detour:
The amount of bending depends on the camera position.
Textureless leaves in Detour:
I have seen this in the high road as well when it is not raining. The leaves are grey like the sky, and opaque.
Non-existant leaves in Detour:
If one looks at the leaves directly, they simply disappear, leaving only the tree trunks visible.