The free one or the commercial one? Alright, so it's a trick question but a fairly legitimate one as Microsoft continues to wage a war against piracy. Let's for a second assume that the person running a pirated version of Office is indeed a criminal and not an innocent bystander that bought it from some OEM email that made it through the spam filters. Do you think they will A) Steal Office 2007 or B) Go legit with OpenOffice?
This is probably the true indication on whether Office users actually use and appreciate most features available in Office 2003 any beyond. I personally do not use even 10% of things beyond Outlook. I'm a very "IT Basic" user and do not even have PowerPoint, FrontPage, Project and the rest of the extended family installed on my main workstation. For me though, Outlook is the glue that holds them all together. With Microsoft integrating the remainder of their family into each and every app, then integrating the entire platform into live.com it would seem that the 10% will shrink to even less.
I've looked at Open Office time and time again and I just do not like it. It feels like Claris Works that we were forced to use on Mac's because the school system made a poor purchasing decision and trained its students on something they will never see in the real world. But in spite of that, I hold on to my Outlook. I use notepad more than I use Word, yet I have this $500 thing on my desktop. So OpenOffice folks, please, why don't you take a lesson from Microsoft interface design team and make OpenOffice 2 look more like Office 2003. If people didn't know there was a difference in what they are looking at (like Firefox), perhaps they would not see the difference and actually switch.