Andrew Chen runs an awesome blog about all sorts of useful web/tech entreprenurial stuff. Recently he made two posts that I wish I had read a year ago when doing financial projections for Fantasy Congress. My own limited experience running a web startup for a year can second what Andrew is saying.

How NOT to calculate ad revenue

Your ad-supported Web 2.0 site is actually a B2B enterprise in disguise

5 factors that determine your advertising CPM rates

While Im at this I should also mention a post made by Guy Kawasaki which outlines the projections vs real costs that Redfin.com incurred during its first two years.

Financial Models for Underachievers: Two Years of the Real Numbers of a Startup