I noticed a few days back that Microsoft have announced that IE7 is to be released to everyone - without the usual WGA checks. Here's something they could do with the data they collect: estimate piracy rates.

A. Microsoft know how many people legally own Windows.
B. Microsoft know how many people upgraded to IE7 under the WGA checks.

=> Roughly, the proportion of people who want to or can upgrade is B/A.

C. Microsoft know how many EXTRA people upgraded after the WGA check was removed (they may have to wait a few months to make this more accurate).

=> There are roughly C * A/B pirated copies of Windows.