Yes could be interesting, merchants get quite detailed reports, as usual the top 5 affiliates account for 90% of sales and those that advertise in context convert better. As for more detailed analysis. I guess its there but I'm only really interested in whether a conversion is made and how they did it as its pretty logical as to why.
Google PPC converts best because you can gear the ad to the product/brand/style etc and those that click on the ad are doing so because they are searching for that specific item.
The slight downside in this business is that unless you are really on the ball with your banners and affiliates are clever in their use of PPC on your behalf, product images or feeds then they will offer a lower conversion rate because the information they serve is too broad.
Hirsh knows this all too well, he would get a very low return if he PPc'd 'mobile phones' or had that text link on one of his websites. We are looking at shopping.com and e-directory as well as they host your whole catalogue for about £1k per year. Good value even if it only converts as well as af.