One of the nice things about virtualenv is that it installs a copy of pip into every virtual environment you create. If you always have one of the environments active, there's no need to even install pip globally.
On my personal machines (effectively single-user), I find there's no need to install packages globally. I have a default virtual environment that I activate in my .profile, and anything that's not project-specific gets installed there.
Not saying everyone should do this, but it works well for me.