In 2008, a random blog, called OddThinking (ahem) tried a controlled experiment to compare glass cleaning products on a troublesome glass shower screen. White Vinegar and Windex were two of the products compared.
I concluded... err... I mean, the researcher concluded that neither did a good job, but Windex had some effect where vinegar had none at all. One of my friends... err... the peer reviewers challenged the result, arguing that the method with vinegar should have been soaking overnight, however that is outside the scope of your question.
There are limitations to this study including, but not limited to:
- Only one type of situation/dirt.
- Not blinded.
- Not published in a peer-reviewed journal.
- The author hasn't publicly declared whether he has any conflicts of interest; but he assures me isn't being paid by lobbyists from Big Creme Cleanser (private communication).
However, it does provide the single counter-example anecdote required to show that white vinegar is not universally the best window cleaner in all situations - that when it comes to my shower screen, Windex is better and that others are better still.