We've taken over management of a site using WP 2.6
We're getting messages about compatibility problems with our server upgrading to PhP 5.3
The client is concerned about the upgrade - the previous developer warned that themes and usability would change during one of the upgrades, therefore they weren't done.
So, asking the hive mind here - are there any concerns with doing this major an upgrade? Anything we would need to watch for? And can it be done as 1 upgrade or would we need to iterate in some of the middle ones?