Patrick Logan, who I remember from comp.lang.dylan days, had this to say about syntax extension:

While Smalltalk doesn't have syntax macros like Lisp, Smalltalk *does* have simpler block syntax and keyword arguments.

The effect is that new keyword messages can take block closures, which essentially delay evaluation until the method behind the message decides to evaluate them, and the message send looks an awful lot like new syntax, very clean.

Many uses of macros in Lisp, frankly, are simply created to hide the appearance of the lambda keyword. Of course there are more "legitimate" uses of macros, but these are less common.

I'd be curious to see some examples of this type of Smalltalk code.