I've been studying the thing for the past month and never really got it. I don't know why but it never added up. The videos here, and a couple of books on theory never helped. some parts always were hard to understand. Last night it all clicked though! I'm so happy. I can finally ramble off the notes in any chord. and my rhythm playing is improved just knowing the fifths by memory.
Before I had to go to the guitar and run my fingers over a major scale pattern and then manually figure out which notes I was actually fretting. took forever. Learning the circle of fifths makes everything so much easier now. Now I can run through the scale pattern on the guitar and just know what frets I'm fretting without having to figure it out first!
I wish I studied this a whole lot earlier