Do not do it! Really, there is no reason to do this. Octave Forge has many packages for different needs but it's unlikely that you need all of them. The common misconception is that the more packages one installs, the more complete and powerful its octave installation will be. However, in the same way one would ''never'' install all perl modules, ruby gems or python packages (because it simply makes no sense), one should not install all octave packages. This isn't desirable and it's not even possible.
Packages should be installed and loaded selectively. Note that some packages are meant to shadow core functions changing the way Octave works, and different packages can have different implementations of a function with the same name, leading to unpredictable results. Others are just broken or crappy and will break your system. What's worse, some of
them packages are even loaded automatically at startup so you may be screwing your octave installation without even realizing it.