A Mathematica package to make up for Mathematica's abysmal built-in auto-save functionality. Once loaded, it will automatically backup any open notebook at user-defined intervals. Configurable, works well...
The package file, NotebookBackup.m, should be saved to the Mathematica user "Applications" folder; for Unix systems (including OS X) this is ~/.Mathematica/Applications. In Windows Vista/7 it's something like C:\\Users\\[you]\\AppData\\... The package can then be loaded by entering <<NotebookBackup` into Mathematica. More instructions are inside the file; note that it may need to be configured for the particular system (paths, etc.) before being used. Mathematica 7+.