Screenshot by Lance Whitney/CNET

Do you spend less time on Facebook than you did six months ago? If so, you're not alone.

A recent survey of Facebook users found that 34 percent of them spend less time on the site than they did half a year ago. Why the cold shoulder?

Those among the 34 percent described Facebook as "boring," "not relevant," or "not useful." Concerns over privacy ranked third on the list.

Only 20 percent said they now spend more time on the social network, while almost half spend around the same amount of time. Among the more than 1,000 Americans surveyed by Reuters and market research firm Ipsos, 21 percent said that they have no Facebook account, leaving 79 percent to answer questions about their Facebook use.

A full 40 percent of all Facebook folks polled use the site every day. The most active ones are those 18 to 34 years old -- 60 percent of them hop onto the site each day. And the least active are those 55 years and older -- only 29 percent of them hit the site on a daily basis.

But perhaps of equal concern to Facebook may be the brush-off being received by products promoted online. A strong majority of 80 percent of respondents say they've never bought a product or service as a result of ads or comments on the site.

That number surprised Gartner analyst Ray Valdes, who told Reuters that "comments and recommendations from friends on Facebook do carry a lot of weight."

Generating ad revenue is more crucial to Facebook now that it's a public entity. The company did bring in $3.7 billion in sales last year, mostly from its online ads. But sales growth has been slowing, according to Reuters.

The company still seems to be feeling its way around the advertising arena.

General Motors recently said it is yanking around $10 million in advertising from the social network, claiming the ads just weren't working.

Other large advertisers are equally frustrated, saying they want to advertise on Facebook, but the company doesn't seem to know how to handle big ad agencies or their clients.

Conducted from May 31 through June 4, the poll received responses from 1,032 people in the U.S.

A Facebook spokeswoman told CNET that the company had no official response to the survey.

Updated 11:15 a.m. PT with comment from Facebook.