Some time ago I wrote this little script in order to track, among different virtual hosts, what is consuming too much CPU:

    #!/bin/sh
    cd /proc
    ps auxw | grep apache2 | grep 'Rl' | sed -e 's/ \+/ /g' | \
     cut -d' ' -f2 | egrep '[0-9]+' | xargs ls -l | grep cwd

Basically this will print a line for every instance of every apache virtual host that is 'running' right now.

It's Linux specific.