[EDIT] Peter Westwood, one of the lead devs, in a comment below suggests against the use of this plugin because of the complexities of the setup process that might be ignored if users install and enable this plugin without following the steps. He points users to the Codex article that explains the setup. If the preliminary setup is that complex, code could be written to understand, walk people through and then validate those setup steps in the future. I am pretty sure the core is going to get more mature about this. So this is just the first step.
Enable Multisite in WordPress 3.0 With One Click!: Sarah Gooding from WPMU.org notifies us of a plugin (which can be downloaded from the WordPress Repository) that will enable MultiSite functionality on your WordPress blog with just one click. Installation for the Enable MultiSite plugin seems relatively simple and the process to enable the functionality is also easy. In case you were not aware of the new MultiSite feature in WordPress 3.0, our very own Klint Finley put together a walkthrough of the feature for you recently.Anyone blogging with MultiSite yet?
Disclosure: The linked blog is run by and advertiser on Weblog Tools Collection