[e12e]

I mostly do this, along with a little hack for certain commands I need, such as mercurial: I have a virtualenv under ~/opt/venv/py-2.7-misc, and make a symbolic link from ~/opt/venv/py-2.7-misc/bin to ~/opt/pybin -- and then my .bashrc checks for a ~/pybin and adds it to the PATH if it exists ( [[ -d "${HOME}/pybin" ]] ...).

So I can just go "pip install -u mercurial", or "pip install <some useful utility>" without worrying too much. And (my) "hg" is in my PATH -- and I can still run stuff in custom virtualenvs on a project basis, just as you say, by specifying the full path (./proj/venv/bin/python ...).

I've never understand why people use anything more complicated.

I do see occasions where activate is useful -- certain packages, I think scipy and pygame are among them -- are not only rather difficult to install via pip, but also tend to be very picky about their environment. Normally I get by by just installing those (and other packages with strong c/c++ library dependencies) via the package manager though.