The Washington Post or Wall Street Journal ran a story on this about 10 years ago, in which a group of reporters traced about a dozen people each of whom adamantly claimed to put in 75-90 hour work weeks. This included a couple of attorneys shooting for partnership, a hospital intern, a couple of small business owners, etc. Each was followed in the normal work weeks and careful work logs were regarded.
As it turns out, none worked anything close to the numbers of hours they claimed. Instead of, say, working TRUE 75 hour weeks, most were found to work something in the 55-60 hour range. This even applied to the attorneys, who were billing an incredible number of hours.
Not saying it doesn’t happen, but it happens far less than most people claim. When I worked in the financial sector (first as an intern, then later as a senior partner before striking out on my own), I routinely claimed to work 90 hour weeks. After I resigned, one of the executive assistant’s told me that she once figured I was really putting in around 65 hours.