Sometimes, I prefer to sit. It doesn't make me less of a fan. And I do find it annoying when someone in front of me insists on blocking my view. Last night some chump in front of me had to stand up so he could text. He had his face buried in his phone, totally oblivious.
Near the end of game 2, two drunks entered our section and played the part of cheerleaders, insisting that we stand up. They were at the front of the section, backs to the court, telling us to stand. They weren't even watching the game. At the buzzer, they left angrily, cursing and blaming us for the Celtics' woes, because we wouldn't stand up. While they didn't even watch the last two minutes!
And personally, I don't care whether Glen Davis or Lawrence Moroney shows up on the jumbletroms telling me to stand up. That's just more of the useless hype. If Garnett stands on the court, and motions for the crowd to stand, that means something. If Davis's video comes on the screen, well, I ignore it. I don't need the "entertainment" staff to tell me how to be a Celtics fan, and when they're on the jumbletroms telling me what to do, even a player is acting as part of the "entertainment" rather than the game.
Stand if you like, if it doesn't prevent anyone from seeing the game. But be courteous of those behind you, and let them watch. At one of the Cleveland games, I had nosebleed seats, balcony row 15. Nobody ever told me "down in front." But when I'm in the front row, I'm conscious of those behind me when the ball is in play.