I recently bought a new computer system, some additional memory and anti-virus software. I spent an hour plus applying for rebates on all of them. There were 5 rebates in all totaling $165. Certainly worth my time and effort, but still kind of a pain in the butt.
Each one asked for a slightly different thing: rebate forms, copies of receipts, proof of purchase seals, original UPC codes, serial numbers, blood sample, etc. Of course it also means scanning everything so that I can have copies if/when the rebates don't come through.
Companies hope you screw up and forget to send something in, or just forget the rebate entirely so they can keep your money. Some companies have also started sending out rebate Visa cards, semi-forcing you to go out and buy more stuff rather than having the cash to pay bills, etc.
When I went to my desk drawer it became clear that I haven't mailed a letter in a while. I found $.39, $.41, $.02 and $.01 stamps. I had to jump online to verify what the current going rate is.
Some companies like Costco and Staples allow you to apply for rebates online so you can avoid the "lost in the mail" excuse. I seem to remember legislation being suggested to eliminate the whole mail-in rebate scam, requiring stores to take care of it at the time of your purchase. That would be worth of the easy button.