From Babsonknowledge.org, the blog by Tom Davenport, Larry Prusak, and Don Cohen:

But maybe my least favorite phrase is "think outside the box." It bothers me partly because I've heard it used 11,580 times in the past 10 years. (I'm exaggerating, but I've heard it a lot.) Also because people who talk about "thinking outside the box" never will. If they could, they wouldn't use a tired cliché to talk about originality. When advertisers parody a phrase ("Think outside the bun"), it's time to move on. [BABSONKNOWLEDGE.ORG: Think You're Thinking Outside the Box? Sorry.]