The latest forecast for Internet advertising is out from eMarketer, which says that in the U.S. it will rise from $21 billion this year to $42 billion in 2011. During that time period, Web advertising’s share of the overall ad market in the U.S will also roughly double from 7.4 percent to 13.3 percent. Another data point: The average person online in the U.S. is expected to spend $114 online in 2007. That number is expected to grow to $199 per person in 2011. The numbers are based on data from the Interactive Advertising Bureau and PriceWaterhouseCoopers. Remember, these sorts of forecasts are almost always wrong. In a way, they are a better measure of current sentiment towards the online advertising sector, which remains exceedingly bullish despite all other forms of advertising struggling or sinking.