In my experience, the biggest obstacle to user conversion from Windows to Linux are the little incompatibilities that trip up users. Some of the incompatibilities may be minor. However, users can get frustrated even with minor issues when they occur often enough or during situations when they are important.
In order not to create unrealistic expectations, I often tell offices and people I advise on this matter that they should expect some incompatibilities and they should learn to work around them or to live with them. This is the price of freeing themselves from giant monopoly and the fear of raids from the software police.
How can I be so sure that Linux/OpenOffice will never be fully compatible with Windows/Office? Because incompatibilities work in Microsoft’s favor. In the past, Microsoft has taken advantage of these incompatibilities to eliminate competitors. IBM’s OS/2 was touted as a “better Windows than Windows, and a better DOS than DOS”, and many independent reviewers and users agreed. Incompatibilities, however, kept cropping up between OS/2 and newer versions of Windows, keeping users from switching to OS/2.
Even if, for the sake of argument, we assume that Linux/OpenOffice manage to become 100%-compatible today, you can be sure that Microsoft will soon release a newer version of their programs containing enough new incompatibilities to cause more problems among free software users.
Microsoft doesn’t take enough care to ensure that their own older versions are fully compatible with their newer versions, why would they do so with competition?
Expect Microsoft to make sure that Windows/Office will stay incompatible with Linux/OpenOffice.
If you want people to stick to free software, do not create unrealistic expectations about compatibility. Tell people upfront to expect incompatibilities, and to learn to work around them or to live with them.