Troubleshooting a failing build can be hard. In TFS Build 2010 Beta 1, you had a Show Property Values link on your build log. This shows the log, but in addition it shows each in/out property for each activity.
In TFS Build 2010 Beta 2, this property is gone. So how can you still get this useful extra information?
As this feature slows down the build a lot, you have to explicitly enable it when you queue your build. Right click on the Build you want to run, select Queue new build and go to the Parameters tab of the Queue Build window. Change the logging verbosity to Diagnostics to get the highest detail of logging during a build.