While EA are keeping Battlefield 3 off of Valve's Steam client due to being 'restrictive' DICE have now confirmed that Origin will be needed on the PC if you want to play the game.
"according to DICEís Daniel Martos
, Origin will be required in order to play Battlefield 3 if the game is bought in retail. We donít know whether this is true if the game is downloaded through a digital download service other than Origin, but we suspect Origin will be required no matter what."
Within the blog it also mentions that there have been issues with Origin draining CPU power while running with Battlefield 3, but they are hoping to have those issues addressed before release.