YouTube is thinking about adding pre-roll ads to existing video clips, and the site's users say they'll think about spending less time there if the site does ad them, according to a Harris poll released Monday.

Harris's research revealed that nearly 75 percent of YouTube's frequent users say they would likely visit the video-sharing site less if pre-roll ads were inserted into video clips; and among those respondents, 42 percent said they would visit a little less often, and 31 percent said they would greatly reduce their visits, MediaPost reports.

YouTube has not said exactly what type of ads it would add to its video clips, but YouTube cofounder Chad Hurley told the BBC that the site is considering adding 3-second ads before the video clips are played.

The Harris Poll also had good news for YouTube: Almost 33 percent of the site's frequent visitors claim that they watch less TV now because of the time they spend on YouTube; 42 percent of online users say they have visited YouTube, and 14 percent say they are regular visitors to the site; 76 percent of males 18-24 say they have watched a video on YouTube, and 41 percent classify themselves as frequent visitors.

WorldScreen.com (via MediaBuyerPlanner) writes that among frequent YouTube users polled by Harris, 66 say they are skipping other activities when on YouTube, including other websites (36 percent), email/social networking (20 percent), work/homework (19 percent), playing video games (15 percent), watching DVDs (12 percent) and spending time with friends and family (12 percent).