I have a moderate automatic preference for Microsoft over Open Source products

Yeah, right!

Michael linked to an IAT Test which claims to be able to find out your unconscious preference for either Microsoft Software or Open-Source software, ruling out self-presentation or controlled responding.
Wikipedia has somewhat more about the Implicit Association Test.

In this case, the participant is asked to please sort stimulus words (Joy, Evil etc.) and pictures (Tux, Firefox Logo, Microsoft Word Logo and similar). By combining "good" stimuli with "bad" attitudes and measuring response time and comparing the results from the test round where "good" stimuli is paired with "good" attitudes the IAT claims to be able to offer insight into a person, regardless of his self-reports.

I am quite wary of tests such as these as I believe them to be useless against a participant who intends to game the test. Especially if the test claims to be objective.

The first trial I did resulted in being attested to have "a strong automatic preference for Open Source products over Microsoft products".
This sounds about right.

The second trial, I tried gaming the system. As the participant is asked to sort the words and images into two combined groups which change, it was clear that the IAT test is based on reaction measurements. If sorting the words into the "Microsoft + Good" group is being done faster by the participant then sorting the words into the "Microsoft + Bad" group (compared to the "OSS + Good" group vs "OSS + Bad" group), it is assumed that the association between good and Microsoft is closer then the association between bad and Microsoft. Thus the user has a unconscious preference for Microsoft.

This much I gathered by guessing and the result was that I consciously delayed my responses at the appropriate time, thus resulting in a slight preference for Microsoft over OSS.

A short Google-Search later I was reading a paper by Klaus Fiedler and Matthias Blümke from the University of Heidelberg confirming my speculation and resulting in the third test run certifying "a moderate automatic preference of Microsoft over Open Source Software"...

So much for the test. :-)