Gray just recently started blogging and has an interesting post about the number of downloads we've seen to date of the compatibility pack. It's a free update that allow people with older versions of Office to read and write the Open XML formats. There are already over 20 million downloads, and as Gray points out the overall number of folks with the update is even larger than that:

The availability of the compatibility pack has been an interesting discussion. Today, the compatibility pack is only available as a manual download. In other words, Microsoft does not "push" the compatibility pack to users using its update tools. IT organizations or end users must manually download the tool, and deploy or install it themselves. Many organizations have (literally) demanded this be made available as an automatic update, while others would be dissatisfied with this, claiming that Microsoft is "forcing" Open XML onto its existing user community.

We decided to make it available as a manual download, and not as an automatic update, and during the first 12 months of its release, the compatibility pack has been successfully downloaded over 20 million times. This means that 20 million people have elected to manually download this 26.2MB software to their computer. This is a significant number of people adding Open XML to their environment.