I couldn’t wait for the final release. I’ve been running the WordPress  Trunk development version from the Subversion repository  since late December, on my laptop. I’ll occasionally update to the latest trunk revision and take a quick look in Xampp to see how progress is coming, since WordPress 2.5 includes a complete redesign of the administration area. The final release date is this coming Monday, March 10th (UPDATE: see this post by Ryan Boren  for my source. UPDATE 2: Release date has been delayed by a week  to Monday, March 17th, tentatively; it’s hard to wait (unless you’re running the beta!) but this is a good thing, they are still doing a ton of work on it!). But I wanted to play with some live data, and I’m too lazy to install all my plugins and export/import all my posts to my test environment, so I decided: it’s close enough, let’s do a backup and install a 2.5 Beta nightly build on this very blog!
You are reading the result of yesterday’s work. I have not found any incompatibilities with my theme. I’ve used the new auto-upgrade feature to upgrade about 5 Plugins to newer versions from right within the administration panel, which works in most cases (depending on the Plugin), and is very, very awesome given the number of WordPress installations I help maintain! I also replaced the aging WP-Cache Plugin with the excellent WP Super Cache , a worthy replacement and an even easier install!
The Akismet  anti-spam Plugin was disabled without me noticing for some reason (I could have clicked it accidentally, I have no idea if it was a result of the upgrade). After getting eight spam comments (only half caught in moderation automatically) within an hour that I had to deal with manually, Akismet was re-enabled in short order with just a click! (Do spammers count as neighbors for that Bible verse? I hope not…although I guess we could “hate the spam, love the spammer,” right? :-)
The color scheme and layout of the Administration area has certainly changed. Some people love it, others hate it. I like more than I dislike. Some things work better, or differently, or more accessibly. Having all areas of the Write Panel available only by scrolling down will take a little getting used to. But the Manage interfaces for Posts and Pages has improved and displays more information in a smaller area, with excellent additional filtering options.
One of the first things to notice when editing a new or old post is that the TinyMCE  visual text editor has been replaced with the new version 3 of the same. I’m enjoying the upgrade tremendously! It works more smoothly, has more options, and has no bugs I can find yet! It adds a full screen composition mode, which makes concentrating on writing a post without distraction that much easier, and it’s available with a toggle toolbar button or the shortcut Alt+Shift+G. On the extended options bar (click the far-right toolbar button in the editor), most of the options remain the same but the Help is excellent if you need it, and there is an “Insert / Edit Embedded Media” button that lets you do just that from a variety of media types, with a preview.
But the best media addition is the Add Media buttons above the editor itself, allowing you to easily insert images, video, audio, and media (like PDF files, etc.) by linking to a URL or uploading. I haven’t tested this much but the interface is slick and I believe it will embed YouTube videos, for example, without you needing to know all the codes or install a Plugin (like I said, I haven’t tested this and I’m not 100% sure). You can also browse the Media Library (also available under its own Manage panel) to insert existing media. This is an area badly in need of improvement and they’ve done a great job!
In addition, you can now Manage tags (without an additional Plugin, although I still like and use Simple Tags ), and the Comments area has been redesigned. Everywhere you go in the Administration area you can see how many moderated comments await your approval, with the balloon count up next to the Comments tab. The method for editing Sidebar Widgets has completely changed. The interface for adding tags to posts has changed slightly. And numerous other changes that are slipping my mind at the moment! So far I have not run into any plugins that refuse to work entirely in 2.5, and I have a lot of plugins installed! (Somewhere in the ballpark of 30 I think).
Come Monday, what do I recommend? Backup your database (and files), do the upgrade, test and see how it works. You can always go back with the backup. If you’re not comfortable with it, wait a couple of weeks to see if the bugs get worked out and make sure that the Plugins you are using have been tested with 2.5 before making the jump. And keep in mind, this is the first attempt at an Administration redesign since 1.x somewhere, so the design itself is like a beta. I’m sure it will get refined in future releases. But I’m enjoying a much more bug-free visual editor, options that make more sense, and a more navigable interface right now!