I think it's been touched on upthread, but the biggest effect I see is medical - not just medical technology but the increased availability of life-saving procedures and medications. Those that natural selection might have deemed unworthy of reproducing may live to do so now, thus keeping more undesireable traits in the gene pool.

Also, in many countries, voluntary population control plays a role. Not everybody who can - and from a natural selection pount of view, should - bear offspring are doing so.

So, even without overt genetic modification, we still are altering our evolutionary path.