A posting on seo-news.de made me aware that MSN seems to manually check the SERPs, too. I went through my logs, looking for the referrer and found the first mentions around the beginning of April and nearly every day since then. Seeing how MSN also returns the e-mail address of the reviewer (firstname.lastname@example.org) in the referrer itself, we can see that there seem to be only two people responsible for the whole of the German index. As far as international projects are concerned, I am surprised that I have not seen the referrer there at all.
If anyone working for MSN should be reading this: With both the e-mail address and provider of the reviewer, it is rather easy to quickly find their Name, place of residence etc. Maybe you should change something there.