Of course it is important. Else, why would you and I stress yourself over it? Despite many b-schools claiming that there is no minimum GMAT score, think about it again. Why would there even be a GMAT if it is not needed? GMAT is a common benchmark to rank our academic ability.
Take a look at the top 50 schools ranked by GMAT.
Look at those above 700 and above. These are your prestigous/elite business schools. They are also your top 10 schools listed in Financial Times, BusinessWeek, USNews.com, etc. Wherever they are listed, you can bet your last dollar that GMAT is an important criterion. Like some said, "getting a higher GMAT score puts you in the consideration list (besides your application essays, work experiences, curricular activities, leaderships, etc.); a lower one puts you in a disadvantage position."
Check the class profile of the business schools you are considering. Study the GMAT score range, and the mean (or median if there is one). You want to aim at least the mean score or higher. I don't think you want to tip their GMAT scale south by being one of those at a lower range (imagine your future classmates are the higher end ones). Gosh, don't I stress you out enough?
Hey, we all want to be in the best. So, show your best and score high.