During tonight's coverage, Jim Courier stated that in his mind the Olympics is the 5th major and the reason why? Because the players certainly treat it that way! He goes on to state that therefore in his opinion Murray was the player of the season 2012. He also says that it's a big reason for Federer to be motivated to make it to the Rio 2016 games.
I'd also rate it as the next important tournament after the 4 majors as well, you can see how much it means to the players and the final is best of 5.
A tournament which doesn't even include close to as many players as a Grand Slam and is best of 3 up until the final can never be spoken of in the same light as such.