I so believe in this.  I remember taking a "how to be the mentor" training early in my career and there were two lists... what a mentor IS.. and ISN'T... the first line on the ISN'T slide was your manager... meaning your manager cannot be the same person as your boss.  I disagree.  Some of my best mentors have been my bosses... and I have tried my whole career to pay that forward.

Here's a bit more of my thinking on the topic from one  of my very earliest blog posts.  http://letsgrowleaders.com/2012/06/25/dont-get-a-mentor/