I got some coupons when I bought my current machine (fp iMac), which enabled me to upgrade to Jaguar from 10.1.4. I had to send 14 GB pounds to cover post & packing.
I subsequently found that this way of acquiring an upgrade doesn't necessarily get you the full whack. There was no Archive & Install facility along with the Jaguar CD's. In all other respects the software was as intact as the fully priced version (I'm sure of that…).
I've got an order in the pipeline for one of the new PB 17"-ers. It will come with coupons for Panther perhaps (i.e. I hope). I'll forego the A & I facility in the interests of economy!