• Total face value of rebates offered in 2008 is estimated to be US$ 6 billion.
• Studies estimate only 10 to 40 percent of consumers collect their mail-in rebates.
• That translates into more than $2 billion of extra revenue for retailers and their suppliers each year.
• Nearly one-third of all computer gear is now sold with some form of rebate. More than 20% of digital cameras, camcorders, and LCD TVs are sold with some form or rebate.
• Unlike an instant-coupon, purchases with a rebate result in the retailer receiving the full purchase
  price up-front.
• Rebates get consumers to focus on the discounted price of a product, then buy it at full price.
• A UF study of more than 1,200 people found participants were "much more likely" to redeem rebates when the deadline was one week as opposed to three.
• The same UF study showed that the more complex the rebate form, the more likely participants
  were to redeem the rebate.

According to this Wikipedia entry: