as this chart from a new Hitwise report shows.
according to the article, the amount of user content available is staggering. Wikipedia has surpassed five million entries. YouTube announced that it had served over 100 million video clips per day.
While the actual participatory visits to these websites are still lower compared to the overall visitors numbers, the share of U.S. visits to the top 20 participatory websites has grown from 3% of all U.S. internet visits in June 2005 to 15.5% in June 2007, a growth rate of 416%. Again there is no breakdown between uploading user content visits versus viewing visits, however, the trend line clearly confirms the rapid adoption.
With travel being one of the favored activities it would not surprise, if a significant share of this traffic is at least travel related. The growth in new travel start-ups using the social networking and user generated content model seems to bear this out.
The full report can be obtained at Hitwise