I wouldn't subscribe to the 100 hrs on type but you do need to feel sufficiently confident that the "duty" you owe to your passenger (to pay them attention and explain what is going on all the time) and the potential risk of distraction from them is within your ability to deal with.
I took my wife on my very first solo flight after I got my license but it was only that I felt confident to do so and that my instructor agreed it was an OK thing to do.
That said, he insisted on doing a check ride first, with Gill in the back and scared the life out of her doing an EFATO.
A driving license can't really be considered to be analagous with flying, otherwise a basic PPL would be allowed "at their own risk" (and everybody elses) out in the dark, the wind, the rain and the clouds without further instruction or testing.
Last edited by Dave Gittins; 6th Oct 2009 at 10:58.