American consumers made a saving of over $17m in December 2010 as a result of using online coupons

"Online Savings in November / December
November Consumer savings* $15.1 million
November Average Discount 27%
December Consumer savings* $17.1 million
December Average Discount 26.8%
*Based on user submitted average savings.
[...]
November Online Coupon Sales

Sales generated through RetailMeNot.com in November Approx. $56 million
Year Over Year Change 27% ($43.8 million in Nov. 2009)
Top Online Coupon $5 off $50 at Target.com
Top Printable Coupon $5 off any purchase of $20 or more for breakfast at IHOP
December Online Coupon Sales
Sales generated through RetailMeNot.com in December Approx. $63 million
Year Over Year Change 26% ($50.2 million in Dec. 2009)
Top Online Coupon $20 Off Entire Purchase Online at Bath and Body Works
Top Printable Coupon Additional 30% OFF Already Reduced Prices at Coach Factory Store"

Source:  RetailMeNot, Janaury 2010

Note - I have no idea how comprehensive this study is.  

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