"However, Microsoft also warned that the beta breaks the Visual Studio Async CTP tool and it also plays havoc with Razor IntelliSense for those punters who have the ASP.NET MVC 3 RC installed."
So, a beta SP1 for VS2010 may break the 'betas' (okay Community Technology Preview, and Release Candidates) of other unfinished add-ons. Hardly surprising (or fair to criticise) - although worth warning people to wait a bit before installing if they use any of those add-ons.
What will happen is that the teams who did the other add-ons will update theirs to work with the new beta. I believe the MVC3 team have said they'll have theirs available on Friday.