The two companies mentioned in this thread, Canon and Tigerdirect, are famous for phantom rebates. See the
Rebate Rogues Kennel at consumeraffairs.com. You can see a long list of complaints by consumers detailing their bad experiences.
Better yet, ask for your rebate at the checkout counter at the time of purchase. If the retailer won't give it to you, refuse to buy. They will eventually get the message.