The Showcase Plugin is being changed. I've disabled the current widget so as to preserve the id's already entered while I figure out how to roll out final changes to the new plugin. I was fiddling last week and forgot to turn it back on again, my bad.
Anyway, behind the scenes the old plugin was causing significant page delays at times as every id linked directly to the amazon page and was rebuilt with every page load - an inefficient workflow at best and the cause of many page load errors or "timeouts"(blank headers and no sidebars at all).
The new incarnation will cache ids, pics, and author details in your blog's database and will not "phone home" to amazon with every page load - very slick in my tests - and no page load errors.
A "reading list" widget is very much one of my favorites, but it is just not ready for "prime time". Anything that depends on "third party" sites, such as amazon, takes a bit to figure out. And sometimes when I think I've got it just right, amazon changes and I'm back to square one.
I've tried to code other tie-ins to amazon's database in the last few years(aka microcontent?) and have never got it "just right." But I keep on trying. Amazon is pretty amazing.