IBM in Sweden is not commenting to Computer Sweden, but Ernst & Young have been using Lotus Notes since the mid-1990's and have been considered a major Notes account. In this first step only the email will be migrated, and it is unclear if applications will eventually be moved as well.
My personal analysis (as I wrote in my original post) is that IBM will not really lose very much revenue, but it is a prestigious win for Microsoft. Even if email might be less important than applications (many consider email a commodity), the market will probably see this as a loss for IBM, and in the long run I think this will be used as another example of "Notes is dead".
I think it is important for IBM to realize that perception is actually important. You can't always be logical. IBM need to keep as many of their big customers on Notes mail as possible, or the market will get the perception that customers are abandoning the platform, even if it is just email.