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The real question that is being posed is, 'Is the level of selection pressure significantly high?'
To us in the developed world, it would seem that it is very low (‘selection pressure’ is strongly correlated with ‘death rate’). In order to debate about this, we need to consider the people who are not successful in passing on their genes (having children). The most common cases seem to be:
Personal choice: Is this a genetically controlled trait? Certainly not! However is there a genetic component that influences this decision? Perhaps; say, genes that result in independent thinking, and going against social norms. But it seems that people who choose not to have children form a very small subset of the people who show these much more general traits. Alternatively maybe there is no genetic component affecting the decision at all. Nature vs. nurture abounds.
Unfortunate Events: Victims of sheer bad luck and circumstances beyond their control who die before they pass on their genes, e.g. a car crash. There are no genes for good luck, so this will not be affected by evolution. I would also include deaths resulting from war in this category.
Disease: Most terminal diseases affect people only when they are older. So these will not significantly affect evolution. However diseases that strike young people also are significant. If there is a genetic predisposition towards these diseases then evolution will strive to reduce and/or remove this predisposition from the gene pool. However the speed of this depends entirely on how widespread the disease is. It will probably be very slow. In comparison the diseases themselves may be evolving if they are caused by viruses or bacteria, and they will do so at a much faster rate.
Impotence: It seems that impotence is covered by what I said in "Unfortunate events" and "Disease". As far as evolution is concerned, impotence is equivalent to death. If there is anything genetic that affects impotence, this could be selected for/against.
Failure to find a mate: This has been the situation most eluded to in this thread. The significance of sexual selection entirely depends on how many people there are who go through their life and fail to find a mate. It is not obvious that this number is significantly high. In such cases it is likely that it is a result of being "too picky", and so this trait may be selected against.
Much has been made of how intelligent/successful/beautiful people have a tendancy to mate with other intelligent/successful/beautiful people. But don't forget that unintelligent/unsuccessful/ugly people also mate with each other. So there is not necessarily a selection pressure due to this 'caste' system of mating. The idea of divergent evolution is ridiculous in this situation as 'intelligent', 'successful' and 'beautiful' are not nearly sharply enough defined and there is enough cross-breeding to keep the species together.
If being unintelligent, unsuccessful or ugly is in-of-itself hazardous to the health then this will effect natural selection directly rather than via sexual selection.
Have I missed out on any? In areas of the world where the death-rate is higher, then the selection pressure will also be higher, resulting in faster evolution. It has been suggested that a genetic resistance to AIDS among prostitutes has been evolved in Africa. (I can't find a reference for this, but I seem to remember reading it some time ago. Can anyone confirm this?).
It is too easy to merely shows ways we can evolve. In doing so, you must also show the ways that we die (childless).
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