Forecasting is extremely difficult. It's especially true for such exploding market as Internet & Online advertising. Historically, every year the market size has been doubled-up. Below are some figures and links where you can find out more detailed market updates

Ad. Revenue Updates

Internet/online advertising revenues ("revenues") surpassed the $1.0 billion quarter for the first time, totaling $1.2 billion for the third quarter of 1999, $726 million or 148 percent growth over the 1998 third-quarter total of $491 million. Revenues totaled $2.8 billion for the first nine months of 1999, more than double the same period for 1998, and averaged over $400 million per month during the third quarter of 1999. Based on historical trends, revenues are on pace to exceed $4 billion in 1999.

(Source: IAB report)