I have been using Office 2007 since the beta 2 at my home.  I love it so far.  I love all the new features and the new user interface.  It seems to be a little slow but that is Office for you.  Other than that I have had no problems with it.

My client installed Office 2007 on their laptop that I use for work with them (since they won't let me use my own because of network security stuff).  When I tried to send a new message from Outlook for the first time after it was installed I got this dialog box [click to enlarge]:

So, I can't send a mail message from Outlook.  I guess it is just a bloated RSS reader and calendar.  Seriously folks, I can't make stuff like this up.  This really happened.  I'm gonna send this into the Daily WTF for their pop up potpourri.