From an emacs-devel message
John Wiegley has a tool called initsplit.el on his web-site for
breaking customizations into multiple files. The issue (I believe) is
why load all the customization information for a package into Emacs if
you’re not going to load the package (at least during this particular
session)? Also, it would allow you to keep the customizations for a
package close to (in the sense of your .emacs files) everything else
associated with the package. Different people (I guess) have
different levels of what they consider to be a “tidy” .emacs file.
I love Emacs.