As a young graduate student, I couldn't wait to publish my experimental results in a major journal. Little did I realize that years later I would see my work in the scientific literature, just not in the manner I had originally anticipated. As a science writer, I now publish papers in the front section of a journal, not the back. After a little over the year on the job, I have found this job to be a good introduction to scientific journalism, and I think working at a journal would be a valuable career launch for any aspiring writer who has a strong science background.
While most people associate "front matter" with the most prestigious publications like Science and Nature, numerous journals have implemented some material in addition to research articles, even if in some cases the features are just short highlights of some of that issue's research. This front content is continually expanding. This rise may be due to journals looking for additional material to maintain readership as searches through external sites or RSS feeds become more commonplace, or as a way to pick up the slack of science's decreasing presence in mainstream media. Whatever the case, future writers should find no shortage of opportunities.
The journal environment is especially a good transition for those who have come in from the research world, in no small part because the atmosphere is still fairly science heavy. The brunt of the work entails reading and writing about research articles as well as talking with researchers about their work. These are tasks with which we are already familiar (and it's a good way to keep up with the scientific literature). In addition, since the audience of a typical journal has more scientific savvy than that of a regular magazine or newspaper, a journal writer can afford to write at a slightly higher technical level. So, for writers who may not be entirely comfortable with their style or who have had no formal training (like academic courses or internships), a journal provides a good transition from technical to creative writing.
As with any environment, there are some caveats to consider, beyond of course the standard jolt of moving from the sheltered walls of academia to a 9 to 5 lifestyle. For one, if the writing position is at a specialty journal, then your writing will exclusively focus on a particular discipline. This may be particularly important since that single-minded focus is the reason I, and no doubt others, left bench work behind. (Fortunately I had the luck to end up at a multidisciplinary journal). In many cases, the journal staff is relatively small, so you won't get quite as much interaction as in a lab environment, and as the front section is usually limited (again, excluding the luminaries such as Science and Nature) and not the primary concern of the journal, the opportunities for personal and creative growth might be a bit limited.
On the flip-side of these limitations, however, is that getting into a journal with nascent front matter could provide you with a chance to develop and expand the content (especially online), and not merely write it. After all, once a journal takes the first step to include front matter, then convincing them to add more becomes a bit easier. From personal experience, though, this process can be a bit slow (sometimes a couple of years to fully get a new feature idea from concept to implementation) so patience is a virtue in this profession.
Working for a science journal may not be everyone's cup of tea, and likely won't sustain a full career. However, for someone who knows their science, likes disseminating articles, and may not be quite ready to be an intrepid reporter or feature writer, a journal is a good place to look, particularly as a gateway to science writing. As many of us lab rats are already familiar with how journals work, and likely know professors who are also journal editors, journal writing is one area of employment where a science PhD has a distinct leg up on the competition. And besides, after spending years trying to get your stuff published, it's a great feeling to be behind the scenes and participating in the publication process.