Patrick Gavin of the Politico put on display an eye-opening contrast on YouTube over the weekend. From February 28, 2008, President Bush made a morning appearance in the White House briefing room and is greeted unsurprisingly with reporters remaining seated.
But on May 1, 2009, when President Obama walks in the room (that would be the "dream sequence" appearance, as an NBC reporter put it), the reporters all stand until he asks them to be seated. You see them rise in the video.
This could be a rather mild outbreak of old-fashioned politeness to the chief. But in my two years in the White House press corps, I never saw reporters in the informal all-business setting of the briefing room stand up to greet the president (unless we were already standing, of course.)
I also noticed that reporters and cameramen were not really comfortable participating in patriotic rituals like the Pledge of Allegiance in the Bush years in East Room ceremonies -- perhaps they equated patriotism with being a Bush supporter?