Office B2TR is a huge improvement in terms speed and memory consumption. In fact, running on Windows Vista RC1 the combination of Office B2TR and Vista RC1 performs as well as XP on my 1GB RAM Toshiba Tecra M4 laptop. E.g., just running Outlook, task manager reports a total of 470-500MB of memory in use, even with Aero Glass enabled. The memory penalty when enabling Glass is totally gone in RC1.
Office presents a cleaned up Ribbon and a zillion little fixes and improvements over Beta 2. XPS and PDF export, however, is gone from the base package, you have to install the plugins already available for XPS export and PDF export.
This is really the first combination of Office and Vista Beta that beats running XP. Users of those 100+ Million Windows Vista PCs to be shipped in 2007 (according to IDC's crystal ball) will like it.