The new plugin directory has been well received and is off to a good start. I have recently added XML interfaces (just send the 'Accept: application/xml' header to the various plugin pages to see it), and the ability for plugin authors to add a password to a plugin entry when creating it to be able to come back later to edit it. Before that I added a scrape-friendly page that allows the Rails command-line plugin script to discover the repositories of plugins indexed at the site.
I really liked the ideas from Trevor Squires on the mailing list about having feeds for every plugin that authors could update and users could track to keep tabs on the releases, etc., of various plugins. I'll probably be adding that functionality next.
Another feature I think would be great is to add searching to the Rails plugin script just like 'apt-cache search' from Debian. It would simply pass the search off to the AWD site and list the results just like it currently lists all available plugins.
There have been other great feature ideas from people on the mailing lists, which I'll be getting to as soon as I can. Feel free to add other ideas to the comments of this post.