From publisher blurb:
Reputation is one of two new level-related statistics introduced in d20 Modern (the other being Defense). To players and mechanics gearheads alike, this is something of a big deal. I mean, something that is always there in the background and changes as you go up, added to the exalted list of base attack bonus and saving throws? Whew. Too much pressure.
However Reputation isn't nearly as important as those other abilities. Why is that? Well it might have been because they didn't want to alter the flow of play too much. Or it might have been because they thought that people wouldn?t respond to something that was too radically different than the d20 they know and love. Or maybe it was because they figured it wasn't broke so there was no need to fix it.
Regardless of the reasoning (and all of the above could have factored into the decision) Reputation has an extremely subtle effect on game play. So subtle in fact that it is avoided by many players and GMs. This article expands on the Reputation rules to make them important, a way to enhance your game and make your character's life easier (or a living nightmare).