Minecraft 1.0 (no more "beta" label attached) is supposed to be released today. However, if you want to keep playing on the server, you must not update yet! The server is still using Beta 1.9 Pre-release 5, and will be updated only when the plugins support structure, Bukkit, is ready in a 1.0-compatible version. This will take some days at least.

If you update by mistake, and want to be able to connect to the server again, simply follow the directions included in my previous post to downgrade.