This post is going to be a bit negative.  For users looking for Enterprise features in the first version of Windows Phone 7, I think I have to recommend wait.

The Office Tab

• No out of box support for SharePoint 2007
• No Windows Authentication (NTLM) for SharePoint 2010 - you will need to activate Forms Based Authentication

http://blogs.msdn.com/b/pstubbs/archive/2010/10/04/developing-windows-phone-7-applications-for-sharepoint-2010.aspx

Exchange

• Same issue as previous Windows Mobile 6.5 in requiring a personal certificate to connect to your corporate Exchange.  I understand this is more secure, but when you could easily integrate with Facebook, Gmail and Hotmail but can't connect to your corporate Exchange it is a bit silly

On a positive note, the WP7 browser is excellent and renders both SP2007 and SP2010 perfectly.