Steve Jobs is back on center stage

Steve Jobs took the stage at Apple's (AAPL) "It's only rock and roll" event today, marking his first public appearance since Oct. 2008.

He was greeted with a standing ovation that lasted nearly 45 seconds.

"I’m very happy to be here today with you all," he told the gathered journalists, Apple employees and high-tech luminaries at San Francisco's Yerba Buena Center for the Arts.

"As some of you know, five months ago I had a liver transplant. I now have the liver of a mid-20s person who died in a car crash, and who was generous enough to donate their organs. I wouldn’t be here without such generosity."

He urged the audience to consider becoming organ donors themselves, as he wrapped up his opening remarks.

"So, I'm vertical, I'm back at Apple and loving every day of it."

Jobs looked gaunt, reports Fortune's Jon Fortt, but surprisingly robust. He spoke for 15 minutes about the new iPhone operating system and the latest iTunes update before ceding the stage for demos and the announcement of iPod price cuts.

He came back at the end of the hour to do his patented "one more thing." The big news today: that on the back of every new iPod nano is a tiny video camera and microphone that allows users to record videos, sync them to their computers and beam them from there to YouTube.

The fact that iPods were getting cameras was not a complete surprise, and neither was Jobs' appearance on stage. A Bloomberg reporter stationed near the back door reported that Jobs walked into the building through a back entrance half an hour before the event was scheduled to begin.