Founder Dilution - How Much Is "Normal"?

Fred Wilson has a post up urging entrepreneurs to record their dilution at exit in a survey being done by Simeon Simeonov. Please can I urge anyone reading this who has experience of exiting to take part. My experience of exits would suggest that Fred's experience is typical when he suggests that: "it will generally take three to four rounds of equity capital to finance the business and 20-25% of the company to recruit and retain a management team. That will typically leave the founder/founder team with 10-20% of the business when it's all said and done."