(Thanks for the info, Mr. Dogood.)
1. All of WP 2.3’s new features have been in MT for years. Tags are the biggest “new” feature in WP 2.3, and there’s still no way to edit, manage, or delete them. MT was one of the first blogging tools to support the Atom API, which is important if you care about supporting web standards. The other improvements to managing drafts have been in MT forever, too.
2. MT’s Dashboard is a lot more powerful and has far better plugins for showing your site data. Instead of just having simple text links, you can show your comments, entries, and tags across all of your blogs (see below) with a pretty graph. There are even plugins for Google Analytics or FeedBurner or hosting your own stats.
3. It takes tons of plugins to make WP do what MT does out of the box. Here’s a few of the ones you’d need to get some of MT4’s features: Advanced Tag Entry, Backup WordPress, Better Comments Manager, Bluetrait Event Viewer, Excerpt Editor, Front Page Excluded Categories, Get Recent Comments, Inline PHP, No Self-Ping, Order Posts, Organizer, Recent Posts, Search Everything, Subscribe To Comments, Tag Functions, Text Control, Ultimate Tag Warrior, Widgets, WordPress Dashboard Editor, WP Calendar, WP-Cache, WP-MU, WP-Vault.
5. You can run all your blogs in one install. Unlike WP-MU, it doesn’t take a separate version of the system to run many blogs, and all the plugins that work with MT work with all your blogs.
6. You can manage all your files and images right inside MT. MT4 has a built-in asset manager, so everything that you’ve uploaded is listed right there, where you can even add tags to your assets.
7. MT is already on version 4.01, and they don’t want to do a 4.02. So you don’t have to wait for 2.31 to come out. As if it wasn’t enough hassle when 2.2.1 and 2.2.2 and 2.2.3 came out, do you really want to go through all of your plugins breaking again like they did with 2.1?
8. MT already has a lot of the most popular WP wishlist ideas built in. Want to search both posts and pages? Need to automatically generate thumbnails for images? Want a more usable photo uploader? Want a better WYSIWYG editor? Those are all built-in already.
9. OpenID built right in. It’s not a plugin, and it even lets you sign in to comment on your blog with a wordpress.com account, or any other OpenID provider. (See my explanation of OpenID.)
10. MT can import all of the content from your WP (and WP-MU) blog right now. And then you’ll have more options of what to do with your blog. You can make PHP pages, sure, but you can also make ASP or JSP pages too.
Update: Make that eleven. (Or seven, depending on how you count.)