Changes the default sort order for posts from post_date to post_date_gmt.
Most people don't need this plugin. Most wouldn't notice a difference if they had it. All it does is change the default sort order of a WP_Query from posts.post_date to posts.post_date_gmt -- that is, sort on the GMT timestamp of a post rather than the local time zone.
Who needs this? People who switch time zones frequently. People running a network installation of WordPress where they want to be able to aggregate posts from all their network blogs easily, and in the right order. I don't know. I wrote it for FreeThoughtBlogs.com, so their "most recent posts" sidebar would stop showing only posts from a few blogs in early time zones. If it works for you, great.
I have every hope that this plugin will be made obsolete by the default sort order being changed in the WordPress core. I can think of no good reason why comments are sorted by GMT but posts by local time.
For all I know, this plugin works with older versions than 3.0. I've only tested it with 3.2.1.