Yes, you don’t require Office 2010 to take advantage of SharePoint 2010. Of course some features such as the Office Upload Center are only available in Office 2010.
Yes, but not all within the office UI. For example, Office 2010 clients integrate metadata and social tagging directly into the UI. Office 2007 users will have to go to the Web UI to populate those things. But broadly speaking, you can definitely use SP2010 with (or without) ANY version of office. I have clients who leverage the benefits of SP2010 for media, for CAD drawings, for Adobe product output… Office is definitely a plus but not a requirement.
OWA provides support to remote users, to users on non-Windows (read:Mac and Linus) systems… wow. HOWEVER I must say I’ve had some challenges UNINSTALLING OWA, so if you’re going to evaluate OWA be sure to do it on a dedicated test server… at this point I can’t guarantee that you’ll not have to wipe the server when you unload OWA. My experience — your mileage may vary.
<i>This question was answered by Spencer Harbar, Enterprise Architect at Microsoft and Dan Holme, Consultant and Trainer, Intellium.</i>