If I take the stats for Amazon UK as an example this is how I have done.
I've had 15570 clicks to their site and this had produced 68 orders where commission has been authorised. So that is an order for every 229 clicks.
I suppose, if you say it quickly, 68 orders doesn't sound too bad but my earnings from this are only £36.28, that's about $72. Now this doesn't sound so impressive.
There are three orders outstanding so the total will go up a little - fortunately one of these is for a television
My figures for Amazon USA are pretty much the same ratio.
I've tried different approaches with Amazon. Everything from banners, widgets, an astore and also context links where they automatically link contextually to relevant phrases within posts.
None of these were really productive.
What I have found works best is if I do the links myself within posts (as I have done in this post). If I write about a celebrity for instance I may link to their DVD
I suppose what this in effect does is to make the links more relative to the subject matter of the post.
I've written before about what I consider to be the power of text ads and links within a post. So far I have seen nothing to make we waver from this opinion.
I'll keep going with Amazon but one of the big things against their affiliate program is the low commission rates on often lowish priced products. Somehow to make money we need to tap into the bigger priced items, like electronics
Just my opinion of course!
Good luck,
Mike.