Just a thought. If you have a nectar card and a Tesco club card its worth signing up to both. A number of my friends have been sent discount vouchers for Sainsbury. You generally seem to get sent the vouchers if its clear you are not doing your main shop there.
A friend used Sainsburys once and a few weeks later got sent a discount voucher equivalent to 10% or so.
Whats people view on this? Should you sign up to all supermarket cards?