As you may have seen on the server lately, there is a notice about updating to Minecraft 1.4. Unless you know how to change your jar (going to your %appdata% folder, making a backup), DO NOT update to 1.4 until Bukkit updates. When Minecraft asks you "Would you like to update?" click "Not now".
You will know it is safe to update when you attempt to connect to Jax and receive a message similar to "Disconnected: Outdated client". We don't know how long it'll take before Jax updates. We have to wait on the CraftBukkit developers (who are usually very fast at updating), and the essential plugin developers (those that develop WorldGuard, ChestShop, etc.) Last time, if I'm not mistaken, it took a week or 2.
It may not be implemented, but vote on what you want the server to do while we wait on the plugins to update.