People who generally play on the server I'm maintaining hate the idea of economy, automatic mining, or anything that differs from what is available on vanilla Minecraft. We use Bukkit for plugins like dynmap and MultiVerse, that gives us more features without compromising the gameplay experience. I have to say that the Bukkit team has done an amazing job of creating a framework to support more features, even for us server owners who like to keep everything as vanilla as possible.
If I wanted to run a vanilla server, I'd still use Bukkit. Better console (in my Linux box, it's a pain to type in the console in vanilla but I don't know if it's just me), antihack plugins, spawn management plugins (so I can make a spawnhouse!), etc.
bukkit is truly amazing, but i'm anxious for the next recommended build for craftbukkit, just cause all the features me and my friends use aren't available until the next build