We run a large multi-site WordPress installation with several hundred blogs and about 5,000 users. We were noticing serious performance problems with the authors widget and upon investigation found that the authors widget was selecting every single one of our 5,000 users, loading all of their information, then only printing out those that had posts on the current blog.
I've written a fix which instead just fetches users that have posts on the current blog, rather than all users. This fix drops the rendering time for the authors widget on our site from 45 seconds to several hundred milliseconds.
Zipped widget with the patch applied:
I'd be happy to submit this patch somewhere, but couldn't find any issue tracker or other place to submit patches for this widget.