I recently converted an old WordPressMU installation to the new WordPress 3.0 with multisite compatibility. WordPressMu is no longer a separate project and is continuing development as part of the main WordPress.org branch under the name ‘multi-site‘ or MS. The reasons for moving over were simple; basically it was a matter of support. Our site has become very dependant on the functionality of WordPress and our users becoming huge fans of the wealth of plugins supported. Any future improvements to WordPress could only be utilised if we moved over to WordPress 3.0 multi-site, and it inevitable to happen at some point so why not sooner rather than later.