UK affiliates need to read Fraser's blog which links out to lots more info.
Basically if your merchant use Google Checkout your sales may not track.
Bad News - Google Checkout UK - Fraser’s Affiliate Marketing Blog
"Google Checkout has launched in the UK but it seems there have been no lessons learned from the US launch. More about that over at the 5 Star Affiliate Blog.
At the moment it seems that customers who complete their transaction by paying using Google Checkout are not going to be tracked by most of the affiliate networks so affiliates will lose out."
GO READ THE REST:
Bad News - Google Checkout UK - Fraser’s Affiliate Marketing Blog