Your users are definitely in for an adjustment as they experience the new UI. Be proactive in training and preparing them. In my experience with clients, organizations that have introduced users to the new UI, with as little as a 30-minute introduction, have found the transition to be significantly smoother than those that haven't prepared end users. Microsoft provides several Office 2007 resources(e.g., training and command-reference guides) at http://office.microsoft.com, which you can incorporate into your enduser training. Once the adjustment is made, the experience of Office 2007 early adopters confirms that the new UI enables users to be significantly more productive. In addition, the new file formats and deployment processes are easier for IT administrators to manage. Most importantly, the power of Office 2007, which includes Windows SharePoint Services and support for technologies such as information rights management (IRM), means that collaboration, knowledge management, business intelligence, and security will add real business value. This isn't just Microsoft hype; I've seen it firsthand. And as Office 2007 rolls onto desktops, we'll all begin to gather real-world experience with the good, the bad, and the ugly in the newest overhauled Office version.