When browsing through folders in ArcCatalog, the modified date and time for all subfolders is changed to the current date and time, even if a subfolder is clicked. This does not affect the files within the folder.
There are files left over from the Beta or Pre Release version of ArcGIS 9.0
Existing machines with ArcGIS 8.3 that upgrade to 9.0 Final do not experience this issue. Clean machines installing ArcGIS 9.0 Final Release also do not experience the issue.