http://www.bankrate.com/brm/news/advice/20041015a1.asp
I took the quiz on "What's your financial giving style?" and after it they had a very intersting statistic:
According to another study conducted by the Forum of Regional Associations of Grantmakers, the value of the average annual household contribution -- in time, goods, money or a combination of the three -- is $1,620. The Forum also discovered that the people contributing the largest portion of their salaries aren’t the ones earning the most. Families with an income of $20,000 to $29,000 average contributions equal to 3.9 percent of their earnings, while those with incomes of $100,000 and more average 2.7 percent. 
