According to PEJ, if Obama had a free ride previously, it was over last week. Partly due to Clinton complaints, and partly due to the perception that Obama is now the front runner, his past record and general fitness as a candidate was the major campaign story last week. Followed by media self-analysis over whether they had gone too soft on Obama. Also of note, with McCain almost certainly the nominee for the Rs, he is declining in press coverage.
Analysis here: http://www.journalism.org/node/10004