Alex Schleber so dislikes WordPress 2.5 that he’s worked out how to patch version 2.3.3 with 2.5’s security patches instead of upgrading. It’s an approach I would recommend against. For one thing, there’s a good chance that one won’t recognize all of the patches via changelogs, if for no other reason than that sometimes new features—not just fixes—have obviated bugs. Also, 2.5 introduced a number of features on the back-end that I would miss.
I am curious about his antipathy towards version 2.5, something he promises to blog about later. My guess is that it has to do with the design of the administrative back-end. That just confirms my opinion that the WordPress admin should be template-able. After all, no one ever decided not to upgrade WordPress because they didn’t like Kubrick.