Mike Speiser, a Managing Director at Sutter Hill Ventures, has a good post from this weekend doing the math behind ad-supported businesses. Worth a read — his argument, that at a $1 CPM, you would need to be the fourth ranked site globally to make $100M in revenues–something that is very, very difficult to do. Mike writes:
We are in a recession. Worse, we are entering a prolonged period of weak consumer spending thanks to the housing debacle and the energy crises. Discretionary marketing dollars (those without a clear ROI) will not grow at the same rate as internet audience — this will lead to an aggregate decrease in brand-based CPMs over time.
If you want to build a real business in consumer, I would encourage you to either sell something (software like Microsoft or Adobe, hardware like Apple, some service like eFax, ecommerce like Ebay or Amazon) or figure out how to build a business that measures and delivers REAL VALUE to advertisers.