[node.js] Where should my npm modules be installed on Mac OS X?

I was attempting to upgrade phonegap via npm when I started running into trouble. Long story short, there are two node_modules directories on my computer.

/usr/local/lib/node_modules
/usr/local/share/npm/lib/node_modules

When I run npm upgrade -g phonegap, it appears that npm updates the copy of the package that resides in /usr/local/lib/node_modules. However, if I which phonegap I find that the symlink points to the older installation at /usr/local/share/npm/lib/node_modules.

Also, when I attempt to install a stand alone package such as express, the files are installed in the /usr/local/lib/node_modules directory, but no symlink to the executable is created in anywhere in my $PATH.

Two questions:

• Which is the proper directory for node modules on Mac OS X?
• How can I configure npm to link executables in my $PATH when it installs software?

Bonus points: Does the method of installing node affect the configuration? There are a lot of options.

EDIT: I figured out that symlinks were being created in my /usr/local/bin, but my .bash_profile was setup with /usr/local/share/npm/bin ahead of /usr/local/bin in my $PATH. I vaguely remember adding that path to my profile at some point, but I'm not sure why.

So the question now becomes: how did I end up with two different node_modules directories on my computer and why would I want to have my node_modules in the share/npm/lib subdirectory instead of right in /usr/local/lib?