For the most part, I've been very happy with the spell checker and thesaurus (synonym) features of Office. One thing I'd like to see, tho, is the ability to spell check and/or lookup synonyms/antonyms from any application. This could be done using a global shortcut that would spell check based on what's in the clipboard or just open a window where you could copy/paste in what you want to check. There are various add-ons and extensions that will add this capability to browsers and other tools, but I want one dictionary/thesaurus that's global. I can see this going into Office or Windows; either way, I'd be happy. If you want this to be provided to everyone, put it in Windows; otherwise, put it in Office. I'm thinking of Word's spell checker and thesaurus shortcuts are F7 and Shift-F7, so I'm thinking Win-F7 and Win-Shift-F7 would be perfect.
There is a tool I found which does this, which was a partial inspiration to this suggestion, but I'd really like to see a global solution with a shared dictionary. Honestly, the clipboard may not be the best data source for this, but it's the only shared location I can think of that wouldn't reach into running applications to pull out data, which I'd see as a security risk.