From the Commentary section of the Wikipedia article on History Commons:

Numerous individuals have given feedback on the History Commons, often praising it for its uniqueness and usefulness.

In October 2010, Salon commentator Glenn Greenwald called the History Commons’s Watergate project a “richly documented summary of those events.” [26]

In a 2009 e-mail to the site, author Philip Shenon, a veteran New York Times reporter and author of The Commission,[27] a book about the 9/11 Commission, wrote: “Your timeline has been invaluable to me over the years. I’m certainly aware of — and flattered by — your citations from my book.” [6]

Craig Unger, author of House of Bush, House of Saud [28] and The Fall of the House of Bush,[29] wrote: “For serious research, it’s hard to think of a more valuable resource than the timelines assembled by History Commons. The material they provide is a welcome antidote to the misinformation and disinformation that has been coming out of Washington in recent years and they are essential tools in assembling a counter-narrative that more honestly addresses the crises we face.” In his acknowledgements to House of Bush, House of Saud, Unger wrote: “The Center for Cooperative Research is another valuable Internet tool. Because I made a practice of citing original sources, it does not appear in my notes nearly as often as it might. However, its timelines about 911 and related issues often helped me find exactly what I was looking for. I highly recommend it to anyone doing research on 9/11 and I encourage its support.”

Author Peter Lance wrote, in the acknowledgements of his book Cover-Up: “As mentioned throughout, I was blessed in this state of my research with access to Paul Thompson’s remarkable timelines from the Center for Cooperative Research … each citation in that database is supported by a news story from the mainstream media. … Any research, reporter, or scholar with an interest in the war on terror would consider the Cooperative Research timelines a bonanza of open source information.” [30]

Village Voice correspondent James Ridgeway wrote in April 2004: “Paul Thompson … is one of a handful of freelance, unpaid, amateur sleuths who have become a 9/11 Information Central — what amounts to an intelligence apparatus aimed at pinning down what the Bush administration knew and didn’t know about 9/11, before and after the attacks. The results of this sleuthing often find their way to the 9/11 families, and in particular, to the by now mythic Jersey Girls, as the leaders of the survivors’ families have come to be called. The researchers are in many ways similar to the team Scott Armstrong, the former Washington Post reporter, recruited in the mid 1980s to uncover the roots of Reagan’s secret Iran-Contra deals. … At the hub of the 9–11 research is [Paul] Thompson’s intricate timeline. … Still other timelines delve into official ‘lies’ from 1979 forward. … [Derek] Mitchell’s aim is to keep the entries as neutrally written and as well sourced as he can.” [4] In his 2005 book, The Five Unanswered Questions of 9/11, Ridgeway referred to Thompson’s book, The Terror Timeline, as “still the most comprehensive summary of the events related to the 9/11 attacks.”[31] At that time, the book contained only a significant fraction of the total amount of information contained in The Complete 9/11 Timeline at CooperativeResearch.org, and a great deal of material has since been added.

New York Magazine correspondent Mark Jacobson wrote in 2006, “[The History Commons’] 9/11 timeline has become the undisputed gold standard of truth research …” [32]

Minneapolis City Pages reporter Steve Perry wrote in 2003 that the History Commons is “endlessly informative.” [33]

Daniel Erlacher, the director of Austria’s Elevate Festival, wrote in an e-mail to the site:

The History Commons is one of the most important and technologically advanced projects of civil journalism there is today. The website of the project is an enormous resource for researchers. Because of the excellent possibilities to tag entities and to group them in timetables, people can easily read and filter information, which is usually presented out of context. The History Commons is a project which helps connect the dots and sheds light on several inconsistencies in official narratives of some of the most important stories of our time. The Elevate Festival was very proud to present the project for the first time in Europe in 2008 and we will continue to support it.[6][34]

Matthew Hurst wrote on his Data Mining blog in 2008: “The site is a cooperative approach to history and presents data in timelines. … I like this vertical approach to wiki data as it has the potential to focus both expertise and data structures, making the data more valuable in a number of dimensions.” [35]

Author David Ray Griffin wrote in the acknowledgements of his book The New Pearl Harbor Revisited

In acknowledging the tremendous amount of help and support I received in writing this book, I wish to begin by mentioning the indispensable source for 9/11-related stories published in the mainstream press: The Complete 9/11 Timeline at History Commons (formerly known as Cooperative Research). … [I]t has surely become, through the continuing work of [Paul] Thompson and his colleagues, the greatest feat of annotated, investigative journal indexing ever achieved on a volunteer basis. Having served as the source of about half of my references in The New Pearl Harbor, this timeline has been equally indispensable for The New Pearl Harbor Revisited.[36]

Matthew Phelan, in an column for Gawker on NSA misuse of authorities, referred to factual information about significant entities and events being “dutifully logged at places like History Commons where … people like to go to collaboratively try and figure out what the hell is going on, post-9/11.” [37]