I think portion control as a diet strategy is not enough. As a training tool, though, I have found/find it very helpful. When I was still eating mostly SAD type stuff, I told myself repeatedly "4 bites is enough" and if I was paying attention, it often was. Then I graduated to "1 bite is enough" and that was true too a lot of times. I do think that the pressure of a calorie budget made me think much harder about what was "enough". If I had just been winging it, I'm pretty certain I would have talked myself into one more (or even more) bite without really weighing what it was worth.
It's also what brought me to primal eating, because when you can't eat unlimited quantities, you pay much closer attention to which foods keep you feeling full and which make restricted calories a misery. I had cut way back on grains before I ever heard of primal.
Now I usually have no problem eating one cookie, one small sliver of pie, one piece of candy. I did eat 6 conventional fig and almond biscotti last week (like some kind of sugar/wheat junkie), so every now and then, portion control fails me. The women I know who have been naturally slender all their lives naturally control their portions most of the time, so I'm not going to write it off just because I can't do it every single time.
CW-125, part calorie counting, part transition to primal
GW- Goals are no longer weight-related