Similar Idea to a Windows search of your hard drive. This would be built into Catalog such that you could select a folder or hard drive and it will search all folders and subfolders for ShapeFiles and Feature Classes in file and personal geodatabases.
Say I have a feature I created for a specific task called SearchToolExplained and it resides in a database or as a shapefile in a folder and I cannot remember where I put it. I could then in ArcCatalog search for SearchToolExplained and it would then search all Shapefiles and databases and find all instances of that Feature Class.