Also, number of SQL queries executed for many operation is lower in WP 3.0, and that directly translates in faster operations. Some things in the admin interface can appear slower due to JavaScript usage, but I can feel that’s slower only in Firefox or IE browsers. Chrome and Opera (my default browsers) browsers are much faster than Firefox so you can’t really feel the difference from older WP versions.

WP speed depends on many factors, and it’s highly dependent on the server configuration in my experience. In all my use of WP 3.0 over past 4 months in most things is faster on my VPS.NET server, but on the other hand, many things are slower on standard shared hosting I have on BlueHost compared to WP 2.9.2. I don’t know exactly why that happens, but problem lies in the limited resources and configuration of shared hosting. Like it or not, WordPress slowly becomes CMS that will be much more comfortable only on VPS or dedicated servers. I will try to make detailed benchmarks on BlueHost, VPS.NET and my development server between WP 2.9.2 and WP 3.0.