I've created an e-Commerce plugin (using WP3.1RC-1) that supports products by creating a custom post type. Ideally this new post type would be displayed like a static page rather than a post, but having looked pretty hard I don't see a way to do that with a plugin in WP3.1. Obviously I can do it in the theme, but that's not great for a plugin as every plugin user would have to tailor their particular theme.
So I will be suggesting to WordPress.org that they extend the customisation of custom post types to offer more flexibility without theme customisation.
Anyway, what is the next best solution? Well, it is to have themes support options that include custom post types. Atahualpa already does this pretty well for posts, pages and certain special pages (e.g. home, categories, taxonomy etc.)
My request is that you provide similar tailoring for specified custom post types. UI might be a section on features that can be tweaked for a custom post type. Within in this are one a set of options that can be tweaked, and space to enter the name of the custom post type to which they apply. One might be enough, but it might be handy to: a) be able to specify more than one set of custom post type options, and b) be able to apply each set of options to more than one custom post type (e.g. enter several custom post type names separated by comma).