In a recent discussion on the OpenOffice.org marketing list, we were looking at some data about MS Office marketshare. As we discovered, market share for office suites is apparently measured based on revenue share. Thus, for a free product like OpenOffice.org, there is no market share. So, we are trying to enlighten users and others trying to get a grasp on this metric. Something like "seats" (same way they measure operating systems) would be more appropriate.
Why is this important to you? Unfortunately, statistics and psychology (perhaps sociology) suggest that many people who hear that MS Office holds 95% of the market for office suites will feel pressure to go out and buy a copy as well so they can "be like everyone else". But if that 95% number is not accurate, then perhaps you are not being like everyone else if you continue to use or buy MS Office.
Benjamin Horst has posted an entry, Marketshare Memes, over at his SolidOffice blog in which he explores some of the information regarding market share. Interestingly enough, this rose out of an analysis of price on office suite selection. I encourage you to read Horst's article. And of course, I continue to encourage folks to try and adopt OpenOffice.org.