Everyone who writes needs to take notes at some time or another. I write fiction as well as non-fiction, and to make my fiction good, I need to do some research.
To serve as an example, I am taking this source material from Wikipedia:
"The Victorian era of British history was the period of Queen Victoria's reign from 20 June 1837 until her death on 22 January 1901. It was a long period of peace, prosperity, refined sensibilities and national self-confidence for Britain. Some scholars date the beginning of the period in terms of sensibilities and political concerns to the passage of the Reform Act 1832. The era was preceded by the Georgian period and followed by the Edwardian period. The latter half of the Victorian age roughly coincided with the first portion of the Belle Époque era of continental Europe and the Gilded Age of the United States.
Culturally there was a transition away from the rationalism of the Georgian period and toward romanticism and mysticism with regard to religion, social values, and the arts. In international relations the era was a long period of peace, known as the Pax Britannica, and economic, colonial, and industrial consolidation, temporarily disrupted by the Crimean War in 1854. The end of the period saw the Boer War. Domestically, the agenda was increasingly liberal with a number of shifts in the direction of gradual political reform, industrial reform and the widening of the voting franchise.
Two especially important figures in this period of British history are the prime ministers Gladstone and Disraeli, whose contrasting views changed the course of history. Disraeli, favoured by the queen, was a gregarious Tory. His rival Gladstone, a Liberal distrusted by the Queen, served more terms and oversaw much of the overall law-making of the era."
Now, this is not plagiarized because I told you I got it from Wikipedia and I am going to tell you I got it here: http://en.wikipedia.org/wiki/Victorian_England today (6-12-13). Now, this is how I would take notes on it:
Victorian England: 20 jun 1837 to 22 Jan 1901 (Queen Vic. reign), linked to Reform Act 1832 ?, Belle Epoque era? Gilded Age? comparable times on continent and U.S., from rationalism to romanticism/mysticism, also Pax Britannica period, Boer War ended (when?), Gladstone? and Disraeli? important Prime Ministers on opposite ends of political spectrum.
Notice that my notes are very brief. Even when I am writing non-fiction I am careful to only grab the points I need for my writing. When I need to find out more, I put a question mark after it. When I know enough about something I do not (note Pax Britannica does not have a "?" after it). When I need all the information a sentence provides I rewrite it in my notes and then rewrite it again in my manuscript.