I launched a web site back in 2004 and used Google Adwords to build up the initial audience. At the time, I was buying clicks for about 10 cents a piece and was able to build a base of users to get the site going. From there its all been word of mouth and search but the cheap Adwords got it all going. The site now has 50,000 users about 10,000 of which are active in a given month. In 2005 I turned on Adsense to try and make some money from this experiment. It made a little money, enough to keep the servers lit up. I’ve since added other ways to monetize and have tried other ad networks but recently went back to Google Adsense for the bulk of the inventory. Why? The CPM has gone way up. In April 2006 clicks were worth about 35 cents on average on this site. In April 2010 they were worth $1.10 on average. Almost 3 times as much! Fortunately I am no longer buying clicks to build audience as that would get expensive quickly but the site continues to grow every day and at over a $1 per click the ad model is yielding good revenue. Wonder what will happen to the price over the next 4 years.