This plugin disables the post revision system in WordPress 2.6+.
While the WordPress 2.6 upgrade has not gone smoothly for a lot of people, one new feature that has yet to bite too many people is post revisions. Whenever you save a change in a post in WordPress 2.6, it saves a copy of the old version as well as your changed version. If you a lot while writing, that can add up to a lot of extra crud in your database.
Now, these can be turned off by editing your wp-config.php file, but that's a bit gross for a system like WordPress where everything else can be done through a nice web interface. This plugin gives you that web-based solution.
Just install and activate this plugin and no more revision debris in your database. Of course, that also means no safety net if you accidentally screw up a post and then save it, but that was the case until 2.6 anyway.