Been to the Office Developers Conference up in Redmond -
What I like:
The Ribbon - can be fully customizeable by a developer.
All Office Docs will now have a new extension (.docx, .xlsx, .pptx, etc) this is because all of the files are now ZIP files - yes you heard it correctly - ZIPpped files.
They did this for a number of reasons - most importantly is the ability to change the file(s) from a Server side process without having to launch the actual application(Word/Excel/...) and just make changes to the DATA (which is in an XML file somewhere in the ZIP)
Also , the file sizes are much , much smaller (not that disk space is an issue.)
Some neat stuff for devs -
I kind of like the new UI - will have to play with it for a while to get a feel for it.