On Snap with Grid priority?...

 From:  Michael Gibson
3561.2 In reply to 3561.1 
Hi Will, actually in v2 there is already something in place to make Grid snap automatically take precedence over "On" Object snap when both are enabled - it should kick in if you are snapping on to a line that is oriented parallel to one of the grid axis directions.

Here's an example - note how the "On" snaps on this line go in grid increments:

It's not really feasible to do this with just any regular curve though, because it would involve quite a lot of curve/curve intersection calculations.

- Michael