What we must do is find a way to live in such large numbers without destroying the planet. We need to switch to green technologies as soon as possible. Things like rooftop gardens and backyard farms (as in raising chickens and small livestock in the backyard) are going to become far more common. We need to find new ways to raise livestock and grow crops that take up less land. Of course, some of the methods for raising livestock in smaller spaces has provided more problems than solutions. Some ideas for raising crops seem possible in the near future. NASA once had program that was working on growing crops without soil. They can be far more tightly packed and they can be grown inside a building rather than outside in the ground. Population growth isn't going to slow enough no matter how much it is regulated. We have to find a way to live on this planet without destroying it.
I second the posts which highlight the necessity to manage resources. I can not figure out, morally, a way to curb the rise of population numbers (nor would I suggest one). Stipulations and regulations made upon the number of births within a family are horrible. Therefore, in order to sustain the growing population, we (as a global society) need to learn to control how we use the resources which are punished by the drastic numbers depending upon them.
My approach to this question is not a very scientific one, but I believe that things have a way of balancing themselves out. This is not to say that we don't need to think about how to conserve resources- in fact, I think that is one of the most important issues to be working on right now. But I don't think the earth will support more than it can handle and will find a way of keeping the balance.
Finding new ways to conserve resources through increased efficiency and through technology seems like consensus so far. We will probably also want to re-think some of our infrastructure strategies, in cities especially, to allow for movement of massive numbers of people through and in relatively small areas.
In keeping with the line of thought in the posts 2 and 3 then, what will should do is put a greater emphasis on research and development that leads to the more effective use of the resources we have. It will probably take more population pressure than we have now to make that happen, but eventually it will have to.
As an interesting side note, China is actually considering adapting its "one child" policy to a two children policy. If that were to happen you would see a quick rise in the planets population within two to three years.
I agree that population isn't necessarily the issue, it is just resource consumption. I recently drove across Texas and I can tell you that the population of Texas could quadruple in twenty five years and there would be plenty of land to support the people in terms of space (that is, of course, assuming they don't all move to a handful of major cities). For that population to be sustainable, however, there would have to be considerable advances in agriculture and energy.
What we should do about it is to find more kinds of technology that allow more people to have a good quality of life without consuming too many resources. Population per se is not a problem. It is only a problem if it leads to overconsumption or other stresses.
Also, in many, many countries, the long term trends are good in that population growth rates and fertility rates are way down.