I have received about 12 Imation rabates since last fall, almost all for CompUSA purchases, and 9 rebates were for CD-Rs. I had difficulty with only 3 of these rebates, one because Best Buy couldn't find the rebate form in the store and kept mailing me the wrong form, another because Imation insisted that I provide a UPC even though the package didn't have one (I e-mailed them scans of the package from all six sides), and the last problem was due to Staples or the post office mailing the rebate check to somebody else.
I was told long ago to glue all UPCs and proofs of purchase to a piece of paper, and lightly glue or tape that paper and the receipt to the rebate form. Also write my name and address and the rebate address and department number on each piece. The dept. no. is more important than the rebate address.