constrained axis vertex snap
 

Is there any way to snap a vertex along a constrained axis to a vertex that is off that particular axis?

This one is hard to explain without having a visual... for example, if you are looking at a box from the top view and the top two corners are not 90 degree angles, is there a way to grab the top right vertex and snap it to the height of the top left vertex to make the object perfectly square?

In Max you can select a vertex and move it along x, y, or z axis and snap it to any other vertex in the scene while keeping it on that axis.

Hope I didn't make this question overly complicated:D

Using your own example, snap to points would work.

1) Make sure you are in Global/World mode in your move tool options (Hold W and Click and hold left mouse button.)
2) Hold V (Snap to Point)
3) While holding V, Click and drag on the move ARROW that you want to constrain. Drag it to the desired vertex. It will snap only to the X, Y, or Z of the vertex you drag to.

This would be cool if we could move and snap in two axis at once, using the small plane rather than the arrow for example.