If you have ever worked with any ArcGIS product, you know all to well the concept of file locking. How many times have you tried to delete an old shapefile or person GDB, only to get the old 'File is being used by another process', yada yada. It always seems to happen to me when I am testing out a new Geoprocessing Tool or trying to delete an old mxd.
Well, Unlocker to the rescue. This handy little utility has saved me endless frustration when dealing with these file locking situations. Not only will it tell you what process is locking your file, it can 'unlock' that process as well so you can delete or rename that file. This gets installed with me wherever I go. Careful on the install though, by default it wants to install 'ebay shortcuts', which is a money maker for the author. I'd suggest a small donation instead.
The other tool that has come in handy in the past is one of the PSTOOLS...psexec. This little cmd line utility will allow you to launch a process as another user. Yes, you can also right click and choose 'run as' but this lets you create a batch file and run it over and over. Why would I want this? Well, I have had a few instances of having to connect to an ArcGIS server as another user to test permissions, etc, and this has been a handy tool to have.