You are trying to install or open an app that didn't come from the Mac App Store but you got a message saying App can't be opened because it is from an unidentified developer. This is how you bypass it.
You deleted everything from your USB key or a drive, so there should be enough free space to copy the new files, but you still get the not enough free space message in Mac OS X? This is what you need to do.
You may have noticed that Facebook ads a the location revealing your wheresbouts at the times you publish post. If you don't want other to know that, this is what you need to do.
Neat little trick to force the preview images of running programs in Windows 7 taskbar or a so called Aero Peek, to show instantly with no delay at all.
If any file can not be deleted, then you can use the program LockHunter, which removes the active connections of other applications to that file, which allow you to change or delete file.
Nice little program that enables you to close all your opened applications and windows with one single click. It works in Windows XP and Windows 7 and doesn't need installing.