I just upgraded to Microsoft Office 2010 from Office 2007 both on my office machines and the ones at home. Microsoft have done quite a nice job of upgrading the office suite. Most of old features have been kept and quite a few ones have been added.
My primary interest for upgrading was the enhancements to the Outlook mail client. Now you can view conversations nicely grouped together just like in the Windows Live Mail client. Actually, I think it works just a little better in Outlook. Having all the relevant emails, replies, forwards etc. grouped together makes it so much easier when replying to emails.
Quite happy with the upgrade and, as is usual for Microsoft upgrades, all my old settings where kept. No hassle whatsoever to upgrade.