WP2.3 was released on September 24th.While WP2.2 didn’t cause too many problems with the introduction of Widgets, this release is different.

In order to make WordPress easier to extend in the future, the WordPress team have changed they way they categorise data - in geek speak they refer to it as the taxonomy schema.

In practical terms this means that the Categories table no longer exists. So any plugins or themes that directly refer to the Categories or Post2Cat tables will break.

Not sure if your site is at risk if you decide to upgrade your site?

I found a useful plugin that you use basically on a once-off basis. You upload it to your site, activate it, and read the report that it generates:

This report can help you locate the plugins that you need to upgrade, and it also analyses your theme to to see if there is any embedded code that could cause problems.

To get this plugin, go to Wordpress Upgrade Preflight Check

Running it before you upgrade could save you a lot of headaches - as you will know which plugins to deactivate or even whether you should delay the upgrade for a few weeks to give the various plugin developers time to implement the necessary code upgrades.