arkyt, when your inktomi contract expires you are supposed to fall out of the index *if* you haven’t been found by their free crawl on its own.
For example, if your site had zero inbound links, when it ended its inktomi contract it would be a 100% certainty to fall out of the index.
I would guess that these sites have a lot of links and should have been found by the free crawl, but perhaps they only have a few and you need to submit the site.
Another possibility is the free crawled page(s) were last crawled a long time ago (months). The content of those old pages, when they were free crawled, is what you will be ranked on… so if you added a bunch of stuff about igloos since it was last free crawled, Yahoo won’t know about it and won’t know to rank you for igloos.
I’d be curious to know one of the awol sites if you want to say.