What "The Secret" has done is put a secular spin, with some shirk, on an already prescribed form of prayer in monotheistic faiths. For example, in Islam, Muslims may ask Allah SWT for a halal wish. The way to do this is: a) believe in Allah SWT, b) ask Him in prayer of your halal desire, c) believe that He hears your supplication and that He will help you (maybe not in a way that we expect it, because after all He knows what is good for us) and d) be grateful regardless of the outcome. Visualization may be a way to reinforce one's desire for something as well as to make strong our belief that the prayer will be answered. However, a Muslim knows, that no matter whether we are aware of prayers being answered or not, we know that we still must be grateful. 
"The Secret" took the same concept of praying to God/Allah SWT, and switched it around into shirk: 
a) it is asking that people believe in "universe," telling people that the "universe" is people's servant and the people are the "true" masters (this OPPOSES Islamic teaching and instruction!)
b) it is asking that people make a clear request (stolen concept from the monotheistic teaching)
c) visualize that you have it and pay attention to opportunities (maybe something new, not part of a religious tradition, but with a lot of scientific support--e.g. positive thinking affects mood, helps people be more grateful about their life and circumstances, confident, etc.)
d) be grateful and not force the outcome--because you can't (stolen from the monotheistic teaching)

Belief in the One--Allah SWT who has created everything is the most important. "The Secret" contradicts istself: it tells people that they are "gods" yet it also instructs them to "pray to the super powerful universe." At the same time, according to "the Secret," this "super powerful universe" is incapable of knowing real from unreal, positive from negative, etc. What a load of cr*p--excuse my language! 

I have been always using Islamic method of making supplication--but must admit that visualization interests me, and I think it can help strenghten my belief in Allah's SWT guidance, help and my gratefulness for His help and everything He has done for me as His creation.