The history data can exported or imported on the "History" ribbon bar. This data is stored in the file named ScanHistory.xml which is stored in you user profile directory under "%AppData%\JAM Software\TreeSize"
Yes, TreeSize can be installed on a cluster. It is not cluster aware, but does not need to be. If you obtain a license for each server and install TreeSize on all machines of the cluster, then you will have TreeSize available at any time on any server of the cluster.Our product SpaceObServer has more advanced cluster support.
This folder is part of the Windows System Restore. You shouldn't delete any files in this folder manually. Its size can be reduced by changing the appropriate setting in the "System" applet of the Windows Control Panel. Windows Vista only allows to turn off the System Restore here. The space used by this service can only be reduced using the Windows command line utility vssadmin.