Probably not. For various reasons, what we read in the mainstream press is unreliable.
Stories are sensationalised by reporters and editors with the effect of distorting information, misleading readers, and rendering the articles in question inaccurate. While the PCC code begins by stating that: "The Press must take care not to publish inaccurate, misleading or distorted information, including pictures"; it is in practice difficult to obtain prompt and prominent corrections from those publishing inaccurate, misleading or distorted information.
Specialist reporters are quite capable of commenting on health and science stories responsibly and accurately. However, they are all too often sidelined by editors when a big health story breaks - and lifestyle reporters are given the task of writing articles about, for example, whether the MMR vaccine causes autism (or whether HPV vaccination has been responsible for the death of a young girl with a tumour). (See here: Bad Science and here: Stuff And Nonsense for more.) These lifestyle reporters often fail miserably, but it seems to me that the responsibility for their shoddy work lies ultimately with the editor who has sidelined a specialist reporter, presumably in order to get a more sensational piece.
The time pressures that journalists face are also a factor in the trustworthiness of the press - according to Nick Davies in Flat Earth News, only 12 per cent of key facts are checked. It seems that fact-checking may be one of the first casualties of a busy news room. There are many examples of journalists being caught out by a failure to factcheck. Here: Lay Science is an example of the media being taken in by a hoax (that "women with big breasts are smarter"), while sports journalists have reported on several unfacts that have appeared on the internet - notably a Wikipedia hoax that claimed of AC Omonia fans that "A small but loyal group of fans are lovingly called "The Zany Ones" - they like to wear hats made from discarded shoes and have a song about a little potato." (See here for more: b3ta.) There's also the footballer who made a "50 Best Young Footballers" list. The player did not, in fact, exist. Moving away from sport, there is a fine example here: How a student fooled the world's media
On the 28th March, Shane Fitzgerald who studies at the University of Dublin, began an experiment which could put journalism into disrepute, by faking a quote on Wikipedia and measuring the spread across the world’s media outlets.
It is worth noting that of all those who fell for Fitzgerald's hoax, apparently only one outlet saw fit to issue a retraction afterwards.
Given the number of sensationalised, inaccurate, misleading, and distorted stories that have appeared in the press - and their failure to fact-check - it seems obvious that we cannot trust what we read in the mainstream media. To quote Mark Twain:
If you don't read the newspaper, you are uninformed; if you do read the newspaper, you are misinformed.
Notes
I have not properly fact-checked this post. You would be wise to be sceptical as to the veracity of the assertions I have made. This disclaimer would be appropriate for many news articles in the mainstream media.
