If you work in an office environment or have more than one PC in your home you might be used to connecting to shared folders across the network. Ubuntu's Places > Network view should show the computers that are local to you and let you connect.
There are essentially two methods used to search for files at the commandline: locate and find. The difference is that locate relies upon a database of files and locations, while find literally searches the file system each time you use it.
GIMP can do just about anything to an image but it can be time-consuming to fire it up just to resize an image. For ultra-quick manipulation, consider Imagemagick, a command-line image manipulation program.
The command-line version of the Disk Defragmenter allows you to exercise fine-grained control over the defragmentation process and uses the exact same program code as the scheduled version.