Paul Thurrott took a look at the latest beta version of Office 2007:
There's been some concern that the new UI will turn off enterprises, particularly, because of possible high training costs. I can't claim to offer any kind of scientific data to refute that, but my own experience with Office 2007 (and the TR) suggests this won't be the huge issue that some think. Indeed, I consider myself both experienced with Office and pretty set in my ways, and I've had no major issues moving to the new software. If anything, the ribbon-based UI makes it easier to find functionality that was previously hidden. My only complaint is that this will lead to the modern equivalent of those "ransom note" documents that cropped up when Apple and Adobe first made desktop publishing possible. But instead of multi-font documents, we're going to see overly colorful charts and graphs..