In another age, sneaking a look at another person's diary, especially a close friend or relative's, was among the great social taboos.
The phenomenal rise of the blog means there is no need to risk causing such offence. The diarists are out in force, displaying their innermost thoughts for the world to see.
And significant numbers of them have come to see blogging as business, in some cases seriously big business.
Blogging has long been known to have influence. It gets people noticed and can get them into trouble if they overstep the limits of free speech in their countries of residence.
But for bloggers aiming to earn a living rather than promote political views, the concept has evolved from the online ramblings of individuals to embrace a vast range of websites covering all kinds of human activity. Ideas and opinions are still traded, but there is also abundant buying and selling.
And every so often, it makes someone rich.
The most frequently cited success story is that of the US website Huffington Post, which began as a blog drawing on published work from various sources.
The founders were Arianna Huffington, a Greek-American author and the former wife of a US Republican congressman, and Andrew Breitbart, Jonah Peretti and Ken Lerer.
Six years after its 2005 launch, Huffington Post was sold to the multimedia giant AOL for US$315 million. Ms Huffington remains the president and editor-in-chief.
But there are many other instances of blogs producing healthy incomes, if on a much smaller scale, among the millions that have appeared on the internet since an early US blogger, Jorn Barger, came up with the term "weblog" in 1997. Eighteen months later Peter Merholz shortened this to blog when he used the phrase "we blog" at his own site peterme.com, which continues today to present "links, thoughts and essays".
Estimates vary wildly on how many blogs there now are. The calculations depend in part on definition; newspaper websites, for example, often seem too grand and wide-ranging to be included although they frequently devote much space to individual writers' blogs. On the other hand, the term has developed to cover more than a single diarist's online articles, with many sites that use the work of several contributors still happy to describe themselves as blogs.
One estimate, from early 2011, put the global total of blogs at 156 million. But web hosting providers report huge growth since then, with WordPress sites up from 56 million in October last year to 68 million now, and Tumblr, recently bought by Yahoo for $1.1 billion, up from 77 to 108 million in the same period.
Advertising is the first obvious source of income for blogs, whether operated by big media corporations or enterprising individuals.
The publisher of Britain's Daily Mail newspaper was late in joining the printed press digital revolution, launching its website in 2004.
This year, as the number of "unique" visitors rose to more than 48 million in one month (just 2 million fewer than The New York Times site), the parent operation Mail Online reported revenue of £45 million (Dh252.4m), outstripping the decline in print advertising for the first time.
Efforts by newspapers to rebrand themselves as multimedia outlets have encountered plenty of teething problems. At first consumers were resistant to online advertising, forcing rates down, and attempts to put editorial content behind "paywalls", requiring readers to buy subscriptions, have had mixed success.
The New York Times is due to report second-quarter earnings figures next month after disappointing returns in the first three months when net income was down by $3.1m from $42.1m on the same period of last year.
Total revenue fell to $465.9m, a 2 per cent drop, with advertising earnings down by 11.2 per cent, from $215.5m to $191.2m.
On one healthier note, while print adverting across the group, which also includes The Boston Globe and the International Herald Tribune, decreased by 13.3 per cent, digital advertising was less dramatically affected, down 4 per cent.
Observers of trends in blogging point to the strides being made online by more modest website publishers.
"The sites looking for advertising revenue and getting millions of hits are just one part of the story," says the British journalist Craig McGinty, who gave up working for newspapers in 2003 and now blogs - in particular for English speakers living in France at thisfrenchlife.com - and advises others on setting themselves up online.
"There are also blogs that cater for specific interests and, through building reputations for expertise and timeless 'how do you' kind of articles, are able to become platforms for selling services and goods themselves.
"I have always said blogging is just a tool. There are plenty out there who make no money directly from their sites but who present their blogs as a shop window for what they can do, whether as writers or providing services or expertise. Work, and therefore income, may then come to them from elsewhere."
Mr McGinty does some work with Phil Voice, the owner of landscapejuice.com and landscapejuicenetwork.com, which are run by Mr Voice and deal with various gardening and horticultural topics. "Income comes via various sources," says Mr Voice. As well as receiving sponsorship from the UK's largest hard landscaping material manufacturer, Marshalls, he sells direct advertising and links within content.
"We have also two membership categories on the network which brings in some income too," he says. "On top of this I've spliced in a number of affiliate reviews and links to products using affiliate links.
"It's tough maintaining a blog with enough fresh content to keep traffic moving. It's even tougher to grow traffic. The secret is being niche but the challenge is to find methods of creating a revenue stream from the content and still staying true to your principles."
The Australian author Jeff Bullas wrote a popular book on the subject called Blogging the Smart Way.
"To make money from a blog in 2013 you do not have to be a Huffington Post. There are many ways to make a living out of blogging that can enhance your current business and lifestyle that are within everyone's reach," he advises.
Among business models he lists are those generating income from sponsorship, charging readers for access to premium content, selling products directly or in affiliate partnerships and online training.
Of those paying their way through advertising, he hails the US-based social media blog and news and technology site Mashable.com founded by a Scot, Pete Cashmore, at his home in Aberdeen in 2005, as one of many selling millions of dollars worth of advertising. In Mashable's case, he says, this is based "almost exclusively on building huge amounts of traffic that makes it an attractive platform for advertising" with about 50 million page views monthly and "dozens of articles a day to feed the content beast".
Blogging for income is, it seems, entirely distinct from the "dot com bubble" of the late 1990s, when new internet-based companies experienced widely varying levels of success and failure. That bubble burst at the start of a new decade. But the blogosphere, as it is often called, marches on in defiance of downbeat predictions that social media would render it redundant.
And it continues to produce occasional examples of entrepreneurial achievement.
Some claims made for potential income seem far-fetched. John Chow, a Chinese-Canadian internet marketing specialist who has been called the world's "number one blogger" and says his internet marketing site's earnings leapt from nothing to $40,000 a month in two years, makes it sound as if anyone can do it without IT know-how or even much work.
But since he makes his money telling others how to emulate his success, and boasts of enjoying an opulent lifestyle, there seems no shortage of bloggers or would-be bloggers chasing fortunes.