The run-time path is a list of directories where ViM looks for files related to its settings, color schemes, documentation and plugins. The current run-time path can be see by typing:
:set runtimepath?One of the directories in the run-time path is $VIMRUNTIME, which on Windows points to the installation directory which contains the ViM executable. For example, it is C:\Program Files (x86)\Vim\vim73 on 64-bit Windows 7. This directory contains the plugins and settings files that ship with a ViM installation. This directory is deleted when ViM is upgraded to a new version. So, it is not a good idea to store any plugins or settings here.
Another directory in the run-time path is $VIM/vimfiles. On Windows, $VIM typically points to the parent directory of $VIMRUNTIME. For example, it is C:\Program Files (x86)\Vim on my setup. $VIM/vimfiles is a good place to place global settings and plugins. The user needs administrator access to place files in this directory.
Neither of the above directories is a good place for store user-specific plugins. On Windows 7, the user needs administrator privileges to add to the above directories anyway. The best place for the user to install plugins is thus ~/vimfiles, which expands to $HOME/vimfiles on Windows. On Windows 7, this is the directory C:\Users\AverageJoe\vimfiles
If the computer is on a Windows domain at work, the $HOME might be set to a shared folder. Access to this non-local directory might sometime be not possible or slow, causing problems if the user places ViM plugins in its vimfiles directory. A good replacement for the work domain is $USERPROFILE, which points to the local C:\Users\AverageJoe even on a domain. The user can set this up as his vimfiles directory by adding this line to his vimrc file:
set runtimepath+=$USERPROFILE/vimfiles