Here is an article from the Guardian, discussing how the UK government is thinking of getting rid of Microsoft Office in favour of open source software. The arguments 1) cost saving, 2) making it easier to share documents.
The article highlights an inevitable trend: the reduced importance of Microsoft Office as the standard for enterprise document creation. But I do not think that some open piece of software will replace Microsoft Office. Unfortunately, we will see increased fragmentation of document creation apps that - I think - will convert their output to PDF files for reading on any computing platform (including mobile phones).
I think that the majority of senior managers at the moment use PowerPoint to view presentations that subordinates send to them, but very few actually edit them themselves.