Please try turning the shaders on, and report problems you may be getting here! Also report if they work fine for you! If it works fine for everyone, next release will no longer force OpenGL 2.0 shaders off.
Stuff to especially watch out for: HUD (if it stays still or rotates wildly), realtime dynamic/world lights shadows (if they have zigzag edges or look fine) and bloom/HDR.
If OpenGL 2.0 shaders do work for you temporarily, follow this procedure to allow the setting to be saved:
Patch the Nexuiz.app or Nexuiz-SDL.app folder:
- Control-Click Nexuiz.app (or Nexuiz-SDL.app), click "Show package contents"
- Open "Contents", then "MacOS"
- Open nexuiz-osx-agl (or nexuiz-osx-sdl) in your favorite text editor
- remove the +"r_glsl 0" from the last line