I have both python2.7 and python3.2 installed in Ubuntu 12.04.
The symbolic link python links to python2.7.

When I type:

sudo pip install package-name

It will default install python2 version of package-name.

Some package supports both python2 and python3.
How to install python3 version of package-name via pip?

Ubuntu 12.10+ and Fedora 13+ have a package called python3-pip which will install pip-3.2 (or pip-3.3, pip-3.4 or pip3 for newer versions) without needing this jumping through hoops.

I came across this and fixed this without needing the likes of wget or virtualenvs (assuming Ubuntu 12.04):

1. Install package python3-setuptools: run sudo aptitude install python3-setuptools, this will give you the command easy_install3.
2. Install pip using Python 3's setuptools: run sudo easy_install3 pip, this will give you the command pip-3.2 like kev's solution.
3. Install your PyPI packages: run sudo pip-3.2 install <package> (installing python packages into your base system requires root, of course).
4. …
5. Profit!