Anja reminds me that Jill asked about PhD rituals. One of the most amusing things about US PhDs is that they wear gowns from a time about twice as old as the country. At Harvard, the gowns are pink. It's great marketing; if you're at an academic ceremony in the US, you can spot Harvard pinks and Yale blues a mile away. Stuff like this makes more sense at Montpellier or Kassel or Oxford, where they've been doing this a long time, but I'm a sucker for non-military pageantry.
People in the US do sometimes fail their defenses -- meaning (usually) that they're sent back for a rewrite. I made it through, much to my surprise, and had a lot of champagne in the laser lab, followed by a nice dinner with Linda.
The best part of graduating, I think, was the moment when they actually read The Words to the School of Arts and Sciences. We artists and scientists got a huge (and unexpected) cheer from our neighbors, the about-to-graduate doctors and lawyers and MBAs; it was the last time the scholars would take precedence, we all knew, and the acknowledgement was special.
It was a nice moment; my last years of grad school weren't pretty.