As a reminder, Minecraft 1.6 is slated to be released Thursday or Friday this week. This next update contains maps and a few other changes (including a huge nerf to fire, sadly).
Typically, this means that Bukkit, the software we use for a number of handy server management mods, is lagged behind by about a week while its developers update the core code for the new version of Minecraft. I tend not to update the server immediately, because Minecraft's server releases are historically unstable for a week or more following a major patch. This time will be no different, and if you update your copy of Minecraft without making a backup, you will likely find that your copy of Minecraft will no longer connect to our site.
So, this is a friendly reminder to make a backup of your .minecraft directory found under %APPDATA%/Roaming/.minecraft (Windows) and ~/.minecraft (everyone else). I would advise against manually updating your client if you still wish to connect to the server.