The winners in the eBay developer contest were announced at ETech, one was Alex Stankovic, who has developed a contextual advertising system for eBay that works just like Google Adsense. I just changed my advert bar for this blog to use his system at ctxbay.
At the ctxbay site you find a link to sign up with eBay for the affiliate program (via Commission Junction) this was an easy fast signup, and gets you an affiliate id number. You then create an account at ctxbay, and enter your affiliate number, which they will then use to call back to Comission Junction and make sure you get paid.
I setup adsense in order to understand it better, and going forward I'll see if ctxbay can generate any sensible eBay items out of the keywords in my blog.