Although Facebook did marginally better this year than last, it still ranked last among all the sites included in the study, called the American Customers Satisfaction Index (ACSI)/ForeSee Results E-Business Report.
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Describing the Facebook user experience as "poor," author Larry Freed wrote that Facebook has benefited from "a monopoly of sorts" in the social networking market.
But Facebook shouldn't rest on its laurels. Despite its dominance, things could change quickly if it doesn't improve its customer satisfaction, according to Freed, president and CEO of Foresee Results.
"If Google can carry over their customer-centric ethos to Google+, Facebook could have serious competition that has the potential to very quickly erode its market share," he wrote in a draft of the report sent to IDG News Service.
Freed noted that Facebook increased its customer satisfaction score from 64 last year to 66 this year -- out of a possible 100 -- a sign the company "may be moving in the right direction, albeit very slowly."
"Facebook is clearly king right now, but if anyone can knock it off its throne, it would be Google," Freed wrote.
Asked to comment on the report, Facebook said it takes user feedback seriously and that it strives to create a "simple, fast and innovative" service that lets people connect with friends safely.
"More than half of our users visit Facebook every day, and we're constantly enhancing our products to offer people the best possible experience," the company said.
Google has said that Google+, which is in a limited, invitation-only trial, has about 10 million members. Facebook has more than 750 million members.
In ForeSee's E-Business subcategory of Social Media, Wikipedia ranked first with 78 points, up 1 point from last year, followed by Google's YouTube with 74 points, also up 1 point. Facebook scored 66, up two points, while MySpace dropped out of the ranking because ForeSee couldn't get enough survey responses from its users.
The survey was conducted before Google+ was launched in a limited beta test about two weeks ago, so it was not included in the study.
In another subcategory, Search Engines and Portals, Google is in the position of the market leader feeling heat from a competitor, in this case Microsoft's Bing.
Google increased its score in this subcategory from 80 to 83, but Bing jumped from 77 to 82, an improvement Freed considered impressive and a sign that Bing's aspirations to make a run at Google are serious. Also making an improvement are Ask.com, up from 73 to 80 points; Yahoo (76 to 79 points) and Microsoft's MSN portal (75 to 78 points).
The third subcategory is News websites, led by FoxNews.com for the second year in a row with 82 points. It was followed by ABCNews.com, USAToday.com, MSNBC.com, CNN.com, NYTimes.com and, in last place, HuffingtonPost.com with 69 points.
Overall, customer satisfaction with E-Business websites increased 2.6 percent to a score of 75.4 points in 2011 compared with last year.