I found the website for the U.S. Bureau of Labor Statistics. They provide a set of tables that break down consumer expenditure by all sort of categories and age. There will be more posts based off this wealth of information, but I found the site looking for average restaurant expenses.
According to the 2010 expenditure table (1), the average household with consumers our age spends $230 on eating out each month. This is for a roughly 3 person household that spends $46.6k annually. Additionally, this does not include alcohol, which adds an additional $40 to the monthly expenses.
It is easy to see how you could arrive at this number pretty quickly. Assuming a 'standard' espresso drink of $3.77 from Starbucks, this would be 1 per adult, per day. At an establishment like Red Robin, where every dish has the same price, you could buy two people dinner ~9 times. As the quality and price of the establishment increases, getting to $230 is even easier.
(1) http://www.bls.gov/cex/2010/Standard/age.pdf 10/4/2011