The use of negative space in design is one of the strongest things a designer can do. Negative space is often very subtle and very aesthetically pleasing. Simple use of negative space seems like a very simple thing, but it is not the easiest thing to accomplish. A designer must be clever when trying to make creative use of negative space. Every part of design should be deliberate, but especially so in designs such as the examples. The designer must be looking for how to change a seemingly plain design into a clever design that is memorable.
The Logo that says "NEGATIVE SPACE" is simple and would be fairly boring if it were not for the hidden "E" between the N and G. The same goes for the "BLACK CAT" logo. It is a simple typographic logo with nothing special, but with the the cat's eyes forming the C's it makes it exponentially a better design.