Mojang has released yesterday a preview version 1.4 for the upcoming update: Minecraft 1.4 pre-release.

However, it will be a few days – typically a week – until Craftbukkit releases a stable update, and perhaps even more until the plugin writers update theirs to work on the latest release.

Internally we have a lot on our hands too, rewriting our in-house plugins to make them work well with the update.

So, with this being said, and given our best efforts I estimate the server will not update to 1.4 until around the end of this month. You should take measures and keep on your computer a copy of the Minecraft you’re running now, to be able to connect and play on