Great post.
One thing that I have always found to be extremely helpful with mixing and arrangement is listening away from the equipment - on your iPod or in a car if you drive, I don't so use the iPod on the bus. Anything that doesn't work will stand out like a saw thumb when listening like this.
Also, personally I find that leaving a mix for a few weeks (if you can) and then going back and listening to it gives me a better idea of weather it really works or not. Sometimes I get sick of something or too invested and judgement goes to the wayside so a reasonable break can help a lot in your evaluation. Of course this only applies if you are making music for yourself and have the luxury of all that time.
RE: Introduction: A good mix is a good arrangement