Wayne, I do my best to make sure all my clients can read H264 files. For years I have recommended to them to download VLC media player if they don’t already have quicktime.
But there are still heaps of people who just have Windows Media player and get confused when it asks them to download a codec. For that reason, if a file has to be made available to the widest audience, a WMV version plus an H264 version should be made available.
Lately I have discovered Miro – an amazingly good free media player that plays full screen HD mpeg/ H264 files much more smoothly than quicktime on windows. It also has a feature that connects you to legal free content from NASA and hi def wildlife & underwater footage. It is cross platform so although you don’t need it on the Mac, it is worth considering if you are coaching clients with Linux & Windows.