People always focus on the everything is an object bit, I remember reading Alan Kay saying that the idea of messaging between parts of the software was much more central than inheritance or even the notion of objects.

http://lists.squeakfoundation.org/pipermail/squeak-dev/1998-...

But I agree that the fact that so much is an object makes Smalltalk so much more flexible. I have not done any real work in Self, so I won't comment.