I've taken the liberty of installing the 2007 Microsoft Office System Beta 1 Technical Refresh on the February CTP on Windows Vista (Build 5308). I took a few screenshots too.
Screenshot: Microsoft Office Word 2007
Screenshot: Microsoft Office Excel 2007
Screenshot: Microsoft Office PowerPoint 2007
My experience so far with the Office 2007 Refresh on Vista hasn't been too bad so far. All the applications seem to work and function with no crashes so far. The "ribbon" applicatioons seem to come up fast and perform nicely with the new UI. I am impressed with how the new UI looks in black and on Vista. I am, however, unimpressed with how Outlook looks in Vista. The black, or obsidian, skin makes Outlook look absolutely terrible. And you can't choose one application in Office 2007 to use one color while the others use another.
Also: the "ribbon" applicatiions aren't using Glass yet in the February CTP.
Screenshot: Word 2007 with no Glass and in Blue
I will talk more extensively of my experiences with Office 2007 and Vista as I continue to test it out. These are just a few observations and first impressions. I still need to dive into the functionality.
UPDATE: As requested, here is a screenshot of how "unimpressive" Outlook 2007 looks in Windows Vista. Now, mind you, this is just how it looks. Outlook 2007 performs great in Vista and some of the updates and enhancements made to Outlook (like RSS) are alone worth using it even if it does look, well - a bit off.
Screenshot: Microsoft Office Outlook 2007