It looks good so far. I've downloaded all the applications, and installed the most important ones first: the essential Office package (Word, Excel, Access, Outlook) and will work on the next ones a little later.
I know the software is not certified to run under a Virtual PC machine, but I decided to go this way - still not confident enough to install a beta over the tablet PC versions I use on a daily basis. So I have created a Windows XP Pro virtual machine with 384MB RAM and installed these new versions there.
I expected very little conflict with any other software for the time being, seeing that this is a fresh Windows XP install.
What I've seem so far looks good. A completely redesigned set of menus, save as pdf options, RSS feeds in Outlook, etc. Since this is my first day with Office 12 Beta I won't post much more until I have more experience. I will be using this Virtual Machine in my tablet PC, so I will try and use it on a daily basis.
By the way, there's a download for backwards compatibility, which allows Office 2003 versions to open Office 12 documents. I will try this for sure.