Since the WP 3.1 is still in beta and many things need to be done yet, I expect that there will be problems with this WP version until final is released. I have noticed a lot of changes each day, so as always, don’t use WP 3.1 for production websites, only for testing.
As for the plugins, dropdown checkbox library (jQuery powered) is updated and loading of JS is fixed for WP 2.9.x. Some display elements are updated also with more fixes in displaying the editors for taxonomies and post types. Also, both editions of the plugin now require at least WordPress 2.9. You can try using WP 2.8, but I can’t guarantee that it will work.
If you have any more problems, please report them in the forum or in comments. Always include exact version of WP you are running, especially if you are using development versions of WP.
GD Custom Posts And Taxonomies Tools: