Teach me about macro lenses

A dedicated macro will give you 2 things, IQ and control in focusing.  The IQ advantage is further enhanced by the additional light available at each F stop, versus using tubes, which rob light.

There are good screw on macro adapters, but they are not exactly cheap, and since they are yet another glass-air gap, there are additional aberrations.  The canon 500D is a good example of this.

I am aware of the effects of diffraction, of course, but for whatever reason I dont really notice it on my nikkor 60g until f/25'ish and even then, its not like looking at a doppler radar screen like a 1.4/35mm at f/11.  I am not sure why that is.