Photoshop: Layer masks should define layer bounds (for alignment and snapping).

I guess I can see how this might be inconvenient to implement, but from a user perspective I see value in the request.
But it might irritate people who use sloppy Layer Masks more than the current behaviour ...

As i was just about to post the same thing pretty much... I'd like to make a modification to this idea? Why not have a button that allows you to enable/disable this feature when directly selecting the layer or vector mask. It could even show up in the layer mask properties.

Then just label it simply along the lines of "Snap bounding box to visible layers".

This would also give people more non-destructive control and allow future improvements to Photoshop to provide more functionality.

Also just have its default set up as to be disabled so that those that want it can have it and those that don't appreciate it... don't. 

Let me add my +1 to this request.
I am currently positioning multiple images on a canvas, creating rectangles the images are used as a clipping mask for the rectangle. This gives me the flexibility to finely tune the remaining parts of the images later => Nice!
If however I want to align all remaining rectangles, they snap to their initial bounds which can be way of e.g. the actual visible center. A toggle switch to influence the snapping behavior would be very welcome. Maybe one could also specify which amount of feathering constitutes the boundary (e.g. 18% feathering or 25% or 0% [which would mean that all of the feathered area is within the bounds, whereas 100% would result in the last pixel which is not feathered constitutes the boundary]