I largely agree with this (subscription required for full text):

The media not only influence public perceptions but also shape and reflect the policy debate. Few decisions are made by policymakers and stakeholders without the media in mind. Given this role and influence, there have long been concerns about distortion and hype in news coverage of biomedicine and biotech. The orientation toward hype is viewed internationally by many scientists, ethicists, policymakers and government officials as the primary shortcoming of the media.

In general, there is a stable baseline level of media coverage of biomedicine and biotech. Much of this news attention is driven by a small number of prestigious and highly influential scientific journals, with science framed in this coverage in terms of social progress and economic growth. Numerous studies of media content have shown that coverage in newspapers is surprisingly accurate, with few errors of commission. Assessing accuracy in the reporting of a single study, however, does not address whether the coverage contextualizes where the study fits within an emerging body of knowledge, drawing comparisons to other studies or expert views. Thus, as a caveat, accuracy in reporting and the dissemination of high-quality evidence are not necessarily synonymous.

This is certainly my sense of the issue. Whether they are rare or not, factual errors are not the biggest problem in bad science journalism. It is the misplaced emphasis, the sensationalization of an incremental advance, and occasionally the 'underdog narrative' pitting the plucky individual researcher against an improperly hostile scientific establishment that makes bad science journalism most damaging. Factual errors can be easy to fix; a flawed understanding of how science operates is not so easy to cure.

While we're on the topic, it's important to point out that science journalists aren't alone in this. The most outrageous recent example of a scientist engaging in this kind of distortion is Jørn Hurum and the Ida fossil: an impressively detailed, but decidedly non-revolutionary fossil has been sold to the public as a major scientific breakthrough in the study of human origins.