This is from my experience trying to use Nsight 3.0 for OpenGL 4.2 Core
Frame Debugger Controls: can’t select “Unit Scale” that part of the GUI is invisible to me
API Inspector: entire interface is frozen, buttons cannot be pressed, and scrollbars cannot be scrolled.
Frame Profiler: Another frozen interface, and occasionally an infinite loading bar in VS.
Geometry: Can view and rotate geometry, can’t interact with any buttons
Pixel History: can’t do anything here
Events: Event list only draws after a resize, and again can’t interact with scrollbar.
Resources: Also need a resize to draw most things, and again can’t interact with anything
Scrubber: actually works pretty well
Shader Debugger: can set breakpoints, but can’t seem to find a way to break on/or select a specific pixel, and values don’t seem to be correct.
The Focus Picker: Seems to actually work pretty well, if a bit confusing at first
Documentation: There is no "Frame Timings" window, and the "How to Set Breakpoints" page refers to HLSL instead of GLSL and mostly HLSL contructs and variables.
Everything that’s in there looks pretty exciting and useful, but sadly at this point most of it doesn’t seem to be usable.