With Windows Office 2010, I believe it now supports .odt files, so OpenOffice/Libre Office and Windows Office can share. The Mac's with Office 2008 cannot read odt files, but you can get OpenOffice/Libre Office for them.
On the email front, I think there is a very good email program for Linux that will talk to exchange, but most exchange servers do IMAP anyway, so that shouldn't be a problem to keep Exchange around for email purposes. A couple of plugin's for Thunderbird and it can handle the exchange calendering features as well. Thunderbird also talks to Google Calendar so either email/calender system.
It will be interesting to see what changes are coming to Ubuntu. Today I would recommend it over Fedora or CentOS for desktop use, but they are changing how the GUI works and that could either be a great thing or a really bad thing.