After upgrading from WordPress 2.3.3 to 2.5 the first, most obvious difference is in the Dashboard. The screenshots below show my [now defunct] Oddity59 blog, not yet upgraded, and TiKouka [now KnowIT].
The colour scheme has changed, information and links have been moved around, fonts reduced in size, and some previously ‘fixed’ items have been made mutable. Overall things seem slicker and sleeker, more efficient and more compact.
A nice touch is the summary of your blog — how many posts and pages and so on. Here’s what mine says right now:
You have 2,325 posts, 12 pages, 2 scheduled posts, contained within 34 categories and 558 tags.
You are using Neoclassical theme with 13 widgets. Change Theme This is WordPress version 2.5.
Immediately below that are lists of Recent Comments and Incoming Links.
Very obvious are the buttons to go straight to write a new Post or a new Page.
Changes continue through each individual Admin screen. New features include a Media Library that displays all the images and other media you’ve uploaded, and tells you which posts they’ve been used in.