What I am looking to do is similar. Consider:
I created a category called "featured" -- all I would do to feature a post is add it to that category (using WP built in UI).
I have found plugins for creating a Featured Post Slider, but they don't seem to be compatible with WP 3.0 (Twenty Ten theme).
Also, the plugins I have found for creating a Featured Post Slider, all seem to use custom fields for the images and the text. Since WP includes a built in UI for "Featured Image" and since the text is already present in the post, I would like to have the text and image used from what is already there.
Alas, I am not prepared to give any help on the filtering of IDs that you propose in your second post, but I will join with you in tackling this issue.
Also consider: If you are not opposed to have a theme handle things for you, and the theme does not hinder you in other ways, the Suffusion theme takes care of all this for you. I cannot use it as I am too much in need of WP 3.0's new menu system, and as far as I know, Twenty Ten is the only theme capable of utilizing the new menu system.